Freehand sliding down on my stomach on a bit of leather on a rope in the marines.
Forward running abseiling from buildings (again in the marines).
Seeing bullets going in the grass right next to me and diving to the ground because we had another short falling grenade is just plain crazy but a good experience
Also sitting a tent in Norway at -54C for one hour and then waking up the guy next to you so you can sleep 1 hour.