I've done a few, mostly very dangerous and unplanned ones, when holidaying with friends. The worst one was a impromptu hike when we took them to Spain.
Now me and the missus usually prefer a more relaxing holidaying, but our friends like the whole 'adventure' element so we decided to go for a walk to a mountain area. And instead of keeping to the path my friends decided to go up some crazy steep route, I'm actually surprised none of us (there were 6 of us) got fucked up. As some of the parts we climbed were obviously not meant for people to go up on without some form of equipment. Getting potentially fucked up on jagged rocks is not my idea of a relaxing time.
Another silly one was the time we went to Sarajevo, and they wanted to go walking off path again (there are still loads of unexploded landmines from the war hidden all around the hills there) So they have paths very carefully laid out with high visibility tape and signs so as to warn people to avoid suspect areas. And keep to the fucking main path.
Me, the missus and another friend got up to a point where we'd had enough, (three hours waking in the hot sun) and said we'd be going back as the others carried on. Their plan was to camp up the mountain with no tents or sleeping equipment so they could see the sun rise in the morning from a really high view.
Anyway 7 hours later they all turn back up to the apartment looking like drowned rats, in their bravado they realised that mountains get pretty damm cold at night, and they had no lights or equipment and were wearing shorts and T shirts, they'd also gone well off path and couldn't find the way back to it, so had to walk back down through the river as the night drew in.
Luckily they made it back to the centre of town before the pitch black nightfall would have really fucked them up.