Pitting your ability against the environment for one.
Riding for days and hours on end with the outback as your backdrop for another. In Alice Springs I spent 7 days riding, shortest day was 3 hours and the longest was nearer 8 with the jaw droppingly awesome outback as my playground. I followed that with a three and a half day guided tour and it was rather un-involving by comparrison.
Technical descents. The rush as you put your faith in to guiding your front wheel through a clear path, picking your braking points and exulting as your get down in record time without breaking any bones.
Technical climbs, getting the body balance just right on the bike so the rear wheel doesnt' slip and the front stays on the ground.
Berming around a bend just so, not skidding at all and coming out faster than you went in.
It's a different sort of fun to riding on the roads but it shore is fun
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