Clytha Castle (Welsh: Castell Cleidda) is a folly near Clytha between Llanarth and Raglan in Monmouthshire, south east Wales. Dating from 1790, the castle was built by William Jones, owner of the Clytha Park estate as a memorial to his wife, Elizabeth, who died in 1787. The castle is an example of the Gothic Revival and comprises three towers, of which two are habitable, and linking, castellated curtain walls. Long attributed to John Nash, recent research has confirmed that the architect was John Davenport of Shrewsbury. The folly has views towards the Sugar Loaf and Skirrid mountains on the easternmost edge of the Brecon Beacons National Park. Described by the architectural historian John Newman as one of the two "outstanding examples of late eighteenth century fanciful Gothic in the county", Clytha Castle is a Grade I listed building.