The Mill Folly Grotto including stone bridge, south of the Afon Llifon

The Mill Folly Grotto, located south of the Afon Llifon, is a Grade II listed irregular rustic rubble garden feature dating from the 19th century. It features picturesque pointed arches and is arranged over two levels. The lower level contains a pool, while a bridge carries the footpath over the outlet into the Afon Llifon. The structure includes a complex series of grotto-like spaces, with an underground chamber accessed by a narrow passage and an additional small chamber at the lower level. The pool is supplied by a reservoir located on the hill towards Fort Williamsburg, connected by a leat from the top of the cascade to the east. The single-arch rubble bridge has voussoirs and a modern timber deck.