While the cave shrine at Phra Nang beach is the best known, Railay has dozens of caves of varying sizes.
The most notable is Tham Phra Nang Nai, also known as Diamond Cave, located a short walk inland from Railay East.
A raised walkway and dim lamps guide visitors through a long passage that opens into a wide chamber with high ceilings, sloped walls and a few stalagmites and stalactites.
Though not the most awe-inspiring cave you'll see in Thailand, it’s worth a peek if you happen to be walking by -- especially if it's raining. National park officials staff the entrance and collect the 40-baht fee.
The Travelfish newsletter is sent out every Monday and is jammed full of free advice for travel in Southeast Asia. You can see past issues here.