My sim loves the rock wall. She went from level 1 to level 10 atheletic in a few sim days. The only problem is that it doesn't register for strength or cardio workout in the atheletic skill, so if you going for maxing out atheletic you still need to workout on the machines.
Presently she's up to "train for Mount Everest" on the wall. Not sure if it goes to anything else.