By far the most interesting thing I've done with a unicycle was to ride it through Laos.
I've been unicycling since 1994. I started out with a borrowed 24" Schwinn, then got my own 24" Miyata. I rode that on trails for a few years, then I got a KH24 off-road monster. For a long time I used the Miyata for transportation and the KH24 for playing around on stairs or debris, but then I got a 36" behemoth for the Laos trip. I also usually play the Bay Area Night Game with the Unibangers, a unicycle team in an otherwise pedestrian-only game.
I got my first taste of rough terrain riding at the first California Mountain Unicycling weekend and went back for more in 1998 and 2005.
For non-Seth unicycling info, head to the Unicycling Home Page or the bustling forum.