By kayak (followed by Blue Lagoon coasteering) from 17 mins:
https://www.itv.com/hub/tales-from-the-coast-with-robson-green/2a4398a0002

There was a book ... The Cave of West Wales.  Unfortunately long of of print but thee is a DVD  which brings this book, bang up to date.  Only ?3.00 in the UK.

https://www.ebay.co.uk/itm/274332682458

Many years ago we kayaked into a sea cave on Ramsey and disturbed a very large seal. I don't think my mate Andy has ever sea kayaked since.