Check out what I did while was on vacation in France! 1140 meter long (0.7 mile) kart trak on the mountain plateu in French Alpes, near Monaco. Altitude is about 7000 feet. Track is owned and operated by one guy... You just pay 40 Euro and get 390cc kart and helmet for 20 minutes. The only problem was that view is so breathtaking it destracts you from the driving at the beginning. It's not as pretty on the pictures, but you get the idea...

http://trusevich.fotki.com/2004/the_trip_karting_in/