So with Lol they went to a ring of ancient standing stones in the middle of a forest in Oxfordshire, on a dark night.
A legend said that those stones would sing to keep demons away. As they unpacked their gear, wondered who had to bring the beers and set the phone that would record the sounds made when they would hit the stones, a band of trolls appeared in the middle of the stone ring and began singing.
Lol, being panicked, asked Gareth to make them stop and they started to hit the stones with the tools they brought. The stones, shaped to emit discords, drove the trolls away.