I think it would be parachuting off the Eiffel Tower and exploring the Paris Art Galleries with some friends. I jumped a little too close to the tower once and ended up on a ledge...then jumped again and SPLAT!!! Fortunately, I walked away and lived to tell the tale!
The good thing about doing this stuff in SL is that you don't actually die....or else I would be in BIG TROUBLE. LOL!