This is the “hermits grotto” at Old Wardour castle, built in the eigtheenth century by a local garden ornaments maker (Josiah Lane of Tisbury).
This is a completely artificial cave and it was made from the castle stones and volcanic lava from Bath. The fossils and water courses inside were designed to make the grotto look like a faerie home – when it reality it was just an overblown version of a garden pond. 🙂
Fantastic.