Flume Trail: I've been on the trail several times. Seems to be more bikes than hikers but never a problem. I always go midweek. And I've hiked the trail in both directions. A shuttle: from Spooner Lake up to Marlette Lake, out on the Flume Trail, and down Tunnel Creek to Hidden Beach at Lake Tahoe. We always leave a car at the Hidden Beach area although parking is illegal at the trail's end. You have to park by the road about 1/4 mile away. And I've done it as an out and back from both directions: from Hidden Beach up Tunnel Creek to Flume Trail and over to Marlette Lake then back down to Hidden Beach - about 16 miles total. Or from Spooner Lake take the fairly new trail up to Marlette Lake and out on the Flume Trail going as far as you like depending how long you want your hike to be. There's a nice spot to stop for lunch above Sand Harbor (that's where my picture is taken from)and then return to Spooner Lake.
