We moved to the Florida east coast from California last year. This place is flat as a board. I have spent untold hours on the stair master trying to maintain some semblance of uphill fitness. I think it's a losing battle.
I'm a competitive cyclist (mountain bike) and I do a lot of time climbing bridges. We'll regularly do bridge rides that have a total of several thousand feet of climbing. There are hills in central Florida if you're willing to go there. When time allows I make monthly trips to to the North Carolina mountains to ride and train. The North Carolina mountains aren't high altitude but some of them are crazy steep. Some of the more extreme events up there you'll get 12,000ft of cumulative uphill over the course of one ride. Getting to the top of the mountain wasn't really difficult. It's aerobic conditioning and a similar muscle group and motion as cycling.
Going downhill though... I don't think there is any way to train for that here. Those muscles aren't used in cycling. It doesn't tax your aerobic system and it wrecked me. I guess you could load up your pack and jump off a box a thousand times a week. But that sounds pretty horrible.
