Kauai is a long way from Mt. Whitney, but people adventurous enough to climb Mt Whitney might really enjoy this hike.  (And anybody Googling for "Secret Tunnel Hike" ought to find this.)   So here's a hike description...

Picture of entrance to the first tunnel
This is the entrance to the first tunnel.  To see all the pictures (plus maps), click here.

Our family went to the island of Kauai, Hawaii in July, 2010, for a vacation.  We enjoyed the usual:  sight seeing, driving up to the Waimea Canyon overlooks, snorkeling and a boat tour.  But the most memorable part for me was finding and hiking the Tunnel Trail.

It is an old trail built in the 1920s for use in creating water diversion tunnels through several ridges.  The tunnels brought water away from the very wet north side of the island, around to the west side of Kauai where sugar cane was grown.  The current trail roughly follows the original route, and you can occasionally see the ohi'a tree split logs lain closely side-by-side (like railroad ties only tightly together).  They probably made a good bed for donkeys or mules to carry supplies to the tunnel-building operation.  The jungle has overgrown the trail most places, and so you only see the logs occasionally.  Instead, local people, maybe hunters, have kept the trail open mostly by use, and sometimes cutting brush out of the way.

I went up the trail twice -- the first day just to find the tunnel entrance.  Having found the trail and tunnel, I convinced my brother-in-law, David, to come along.  Unfortunately, day two was rainy, unlike the first.  We got very soaked, and slipped and slid all over the trail.  I thought, during the second day, if it had been that wet the first, I may not have gone back.

On the first day, I encountered a couple and their daughter, 7, from Thousand Oaks, CA:  Debbie and David A.  They had spent the night at a bamboo grove by the Hanalei River.  The couple had hiked it 10 years before after hearing about it from local kayak rental people.  I was amazed that their girl was doing so well -- she made no complaints.  They were carrying super light packs -- they used hammocks and thermal blankets for sleeping.

Picture of 9 hikers and their dog. On the second day, a group of 9 adventurous Hawaiians caught up to us at the Hanalei River.  Most were from the mainland, but living and working on the island.  It was the first time in for all of them.  Note their clothing -- it worked for them!

Guidebook:  Planning for this trip, my wife found a book, The Ultimate Kauai Guidebook, Kauai Revealed, by Andrew Doughty.  (He's her favorite guidebook author.)  In the book, he describes the "Secret Tunnel Hike" to the North Shore.  The part about the North Shore is a bit misleading.  The tunnel leads to the Hanalei River, which flows to the north shore, but the tunnel is high on the mountainside.  If you go on this hike, you should get this book.  I couldn't have found and followed the trail without it.  In fact, I photocopied his map and description, and carried it on the trail, referring to it several times.  Even if you don't go on this hike, the book is great for finding so many good places to see on the island.

Driving to the trail:  See/print the maps at the end of the set of pictures.  Google Map link here.  Take State Hwy 580 from Wailua to its end (where the pavement ends), then continue about 3.5 miles on the dirt road.  I took a small rental car on the road--just go slow over the potholes.  If you have a roadmap gps, set it to "Keahua Arboretum" (where pavement ends).  It takes more than 30 minutes each way from State Hwy 56.

Hiking time: Our times:  2.5 hours to first tunnel. In first tunnel, to the river, ~1 hour. Second tunnel ~30 min. Round trip (car to car):  8.5 hours.  First day, I made it to the tunnel in 1:45.

Shoes & Clothing:  The Hawaiians who went wore light shoes and even Tevas.  I wore trail runners and hiking socks -- they were comfortable and cleaned up nicely in a washing machine.  Forget anything waterproof, you're in 2 feet of water in one section of the second tunnel.  Shorts or hiking pants.  They might get ripped if you fall.  I never got any scratches on my legs wearing shorts, even with a few falls.

Insects:  The guidebook talks about taking repellent.  I took none, and never saw a single mosquito.

Walking sticks:  They can be helpful.  We cut several bamboo sticks at the Wailua river crossing.  Unfortunately I broke one in a fall, David broke two.  They have no lateral strength.  We cut some from tree branches, and they lasted.

  Following the Trail

picture of muddy 4wd trailFrom the parking area, the trail starts as the 4wd track (the right leg of the Y).

picture of wailua river crossingIn about 5 minutes this track ends at the Wailua River (north fork).  The river was mostly dry the first day, but I waded the second, since rain had increased the flow considerably.  We cut bamboo walking sticks on the far side.

The route is straight ahead in this picture, then left a little once across the river.  The path generally follows the river upstream just a little, then veers away.

This is the path, not a maintained trail, but not too difficult to follow.  I put the camera away after this, since everything was wet due to the rain.

After the river, the trail crosses four streams.  The first two are quite close together, then a third.  Near the middle of the hike, there are several old electric poles still standing, one with insulators and thin wire hanging. I am guessing it was used for telegraph or phone communications.

Next pictures are at the fourth stream.
picture of the muddy overgrown path

picture at the fourth streamThe fourth stream is in an open area, out of the dense forest cover.  The path does not cross, but follows the boulders upstream, and continues on the left side.  It finally crosses about 100 yards upstream, just a few minutes from the first tunnel.

At last, the first tunnel appears! The first day, it took about 1:45 to get here.  Second day took longer since we stopped more often.

This tunnel is over 4000 feet long, but as soon as you step inside, you can see the light at the other end!  This is easier to walk through than the second, since the water is never any deeper than at the entrance, and there is always ample headroom.

At the far end where you see the light, you do not exit; instead, take the branch to the left, and walk another five minutes or so.  The branch actually changes directions three times before you exit into the feeder canal on the side of the canyon.  I did not get a picture, but watch for the point where you climb out of the canal and head down to the river.  (Not sure what happens if you try to follow the canal--seems like it should come out near the dam.  If anyone reads this and then takes the hike:  PLEASE email me and tell me what happens if you follow the canal.  I'll report it here. ...in fact, I need a picture of that area, too.)
picture at the tunnel entrance

picture of people crossing the Hanalei RiverAfter exiting the canal, the path descends quickly to the Hanalei River.  This involves sliding down a ten-foot drop, where you hang onto tree branches and roots to make the descent.  Once past that you come out to the river and a monstrous house-sized boulder.  This picture shows a part of the boulder on the far right.

Once across the river, follow the path upstream through the brush, then veer left and come out just below the dam (less than five minutes).  Climb the rocks up to the top of the dam, then look for the path to the right of the dam.  It quickly leads to a concrete wall and the entrance to the next tunnnel.
picture of water flowing over the dam

picture of ladder dropping into second tunnelHere is the ladder leading into the second tunnel.

This tunnel is not as "clean" as the previous one.  The water is deeper right away, and some distance in, there was a cave-in during the tunnel's use.  You will first see rock from the cave-in stacked neatly along the side of the tunnel.  Then at the cave-in (the ceiling collapsed in a weak area) there is still quite a pile of debris.  This pile slowed the water flow, and the incoming water dropped lots of silt.  So walking beyond the pile, the water is up to 2 feet deep, and you are walking in deposited silt -- not as bad as the slick mud outside.  In this deeper area, there is a section where you must negotiate over a few wooden braces placed to shore up the tunnel.

This tunnel also branches left near the end, and like the first, makes several turns.  There is even a short incline completely lined with concrete (bottom, sides, top) to crawl up.  Fortunately it is not slippery.  And there you exit to Ka'apoko Stream

This place is one-of-a-kind!  A waterfall coming through a slot; moss and ferns everywhere.picture of waterfall

picture of overhanging wallsHanging roots and water dripping from overhanging walls; even tree ferns.

Looking up, there are green pinnacles above a red-flowering tree.  (An invasive African Tulip tree)

Enjoy the sights -- very few people ever see this spot.
picture of blooming tree

Here's a video of the waterfall...

Here is a link to my annotated Google map showing the road from the main highway around the island to the trailhead.

At the end of the set of pictures, there are three maps you can print. (View the "Original" size image, and use landscape mode to print.)  The first map shows the road, trail and part of first tunnel.  The second one is zoomed in, showing all the trail. The third one shows the tunnels.

The maps were developed from this link.  Dead center on that link shows the trailhead.  Click the various options in the upper right corner.  Best are T4 Topo High, Terrain, Map and Satellite; several show lines for the tunnels.  Several also show the original trail!  Here's the same map, but centered on the final destination.  Note there are two dams labeled with the northern one blocking two small streams.

Here's a good mapping web page, with the waterfall in the center crosshairs.  This map can be changed so you can see multiple modes:  Google's "map" and "terrain view", MyTopo, and satellite.  Gmap4 Map

Please note:  At the end of the trail, the maps show a third tunnel.  A short one, starting near the base of the waterfall.  If you go, look for the entrance.  It will be just across the dam from the waterfall.  It leads through the next ridge, where the map shows another dam.  See the next picture and text below.  Unfortunately, the tunnel ceiling has caved, damming the tunnel so it is filled with water.

Just beware:  The secret tunnel "trail" is quite treacherous.  I slipped and fell the first day, jamming my thumb into a log.  At first I thought maybe it was broken.  It wasn't, but it is still sore, two weeks later.  On the second day, I slipped and fell, punching a rib on a snag sticking up from a log.  The bruise was still ugly two weeks later.  Swelling in my calf was finally receding where I bruised it in the same fall.  David had a tough time, since his glasses were always fogged up and wet.  His pants were ripped, but he had no injuries.  The first day, I saw another hiker with ripped pants.  On the second day, one of the Hawaiian hikers re-injured his ankle.  David had talked to an associate from the Sacramento area who actually broke his leg on the trail.  I believe it!

Also for your information:  Leptospirosis (or Lepto) is a relatively rare disease in humans, but can be contracted by prolonged immersion in water or contact with soil containing urine from infected animals (rats, mice, dogs). Beginning symptoms (2 to 20 days after exposure) are flu-like -- fever, chills, muscle pain, intense headache. Untreated, it attacks the internal organs. Leptospirosis on Wikipedia  The International Leptospriosis Society reports that Lepto can occur in 1 out of 1000 people in high-exposure groups (ie. in tunnel hikers).

Regardless of the warnings, I'd still go on this hike.  But the choice is yours.  For myself, it was truly a great adventure -- a once-in-a-lifetime memorable day.

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Edit: Adding a little more info:

Here is a blog from Andy at http://great-hikes.com/ (aka KauaiHiker)
Kaapoko Tunnel Hike, Part 1   Good pictures of some of the highlights of the trail and tunnels.
Kaapoko Tunnel Hike, part 2   In Part 2, Andy actually found the third tunnel.

And here is his picture from the third tunnel looking out to the waterfall:

He writes:
"Back beneath the overhang, we found the entrance to the mythical third tunnel. This one is more roughly-hewn, nowhere near as well-shaped as the other two. It does have 3 windows, as it seems to run parallel to the valley at first.
The tunnel turns left to go under the ridge, but is blocked shortly thereafter by a large rockfall. The rock that has fallen from the ceiling is soft and spongy, not a good material for tunnels. You could climb over it, but the water on the other side is deep and no exit is visible, so my preservation instinct told me to turn around here.

So the "water to the ceiling" is caused by a dam created by a ceiling collapse within the tunnel. Looking on the map, it seems like one could walk downstream in Kaapoko stream to the junction with the other stream, and then walk up that stream to find the far entrance to the tunnel, plus the diversion dam. ...Maybe some day.

Looking at various maps, especially Google's "Map" and "terrain view", you can see the dam labeled on the other side of this last ridge. In fact, there is even a short canal, maybe 200' long, bringing water along the canyon side to the dam from yet another stream! I'd love to go explore the remains of these works sometime.

. . . . . . .
Two videos on YouTube from skjos96 showing the trail and tunnels. He's a much faster hiker than me.
  Secret Tunnels of Kauai (Kaapoko Tunnels) - Part 1
  Secret Tunnels of Kauai (Kaapoko Tunnels) - Part 2
. . . . . . .

Recent discussion on http://www.tripadvisor.in/ can be found here: Secret Tunnels Hike

A report from 2005. Excellent pictures, but only through the main part of the first tunnel and the spur that turns left (he calls it the second tunnel).

A better map, from "The Trail of the Ancients"

Some Vimeo videos:

This shows a good video of the "trail".  Hiking To The Hanalei Tunnel - Kauai

This video shows lots of footage inside the tunnel.  Tunnel Hike Kauai 2010

Here's a video of a guy and his wife on day 2 of their honeymoon hiking the trail to the first tunnel.  Shows the conditions pretty well.  Pretty comical--they weren't the best prepared.  Death March Monday

Here's a YouTube video added July 2012. These guys hiked in a steady rain, and couldn't cross the river after the first tunnel due to the water level.   Kauai, Wailua Tunnels to Hanalei, "secret" Kaapoko tunnels.