I found this mountainboarding video game that seems to be pretty cool, its called sewer run and there are currently 1,943 players playing it which is pretty amazing.
Heres the specs for this mountainboarding video game:
Sewer Run
Pick your player, choose your board, and get ready to grab some air! Mountainboarding goes underground in this awesome sim that challenges you to ride some of the worlds longest open sewer runs. Score points by pulling sick tricks, race your opponents to the end of the run, or take them down with weapons you collect.
Shred your way to mountainboarding fame!
Instructions
Use your keyboard arrow keys to steer. See in-game help for detailed instructions and other key commands.
Minimum Requirements
Windows 98/ME/2000/XP
Pentium III 1.5 Ghz
64 MB RAM
3D Graphics Card with 32 MB RAM
DirectX 8.0
Sewer Run Credits
Developed by: Kinelco