We recently came across this video and had to find out more. Above is footage of Lutz Eichholz and accomplice Stephanie Dietze putting a new spin on mountain biking down the Dolomites. The mountains are still there, but the vehicles of choice is are unicycles. 

Eichholz hails from Kaiserslautern, Germany (near where I used to live). He is world champion unicycler and is listed in the Guinness Book for some of his feats.

More, including photos and other videos at his blog (available in English and German).