I was in a group of about 30 riders on the Costa Blanca. We had just hit a small hill and were starting to power our way up it when we heard a loud noise and a stream of expletives coming from the back of the group. A rider had just tried to change gear and his gear hanger had broken, sending his rear mech into the wheel. Several spokes were broken, his mech was hanging down into the wheel and the chain was mangled. We were about 30 miles from our hotel, in the middle of nowhere.
Between us, we managed to take off his rear mech, shorten the damaged section of chain and turn his bike into a singlespeed for the ride back, and straighten his rear wheel enough to make it rideable with the back brake slackened off.