We visited this place yesterday. It is under the main street in Royston, Hertfordsire in the UK.
The cave carvings were done around the 1350s. No one knows what the cave was originally for. Possibly Templar, maybe Masonic, maybe an early hidden church or hermitage. It was lost and forgotten till the mid 1700s. No documentary records exist about it. Great visit and only £4.
The graffiti is from the 1750s onwards. The original 14th century carvings include St George, St Catherine and St Lawrence. Also crucifixions and many Templar/Masonic symbols.
Click any of the pics for a larger view.