St Trillo’s Chapel, Marine Drive, Rhos-on-Sea, North Wales. This tiny building is thought to be the smallest church in the British Isles. It has enough seats for just six people. The chapel is named after St Trillo, a 6th-century saint. The spring inside the chapel provided St Trillo with drinking water. You can still see the well in front of the altar, if the chapel is unlocked. This water source would have influenced his decision to build his cell at this spot. For centuries, this well supplied the water for baptisms across the extensive medieval parish of Llandrillo. It also had a long tradition of being a healing well.