With hindsight, the potential consequences of some of the activities were not thought through.
We would cycle to a disused mine and after an explore of the site we had visited many times, would play on the slag heaps. - This was pre land restoration and other than sealing the shaft and dropping the tower, the rights owner just seemed to have walked away from the site many years earlier. Find a sharp, rusting sheet of disused metal, bend it a bit and then climb one of the heaps. Sit on said sharp rusting metal and slide down.
Or riding to a wooded area we knew where there were mature trees on the side of a steep hill. On one of the branches, someone with even less regard for their personal safety than us, had tied a length of rope of around 6 metres. Due to the steepness of the hill, the size of the tree and the length of the rope, with a decent swing out, it was easily possible to be 10 metres from the ground. It paid to hold tight as the nearest road, should an ambulance have been necessary, was around half a mile away.