While the group tour experience is tacky, and the guided chit-chat pleasant but mostly uninformative, the actual geological phenomena visible in these two dramatic caves is worth the price of admission. Superstar Beyoncé loved them so much during a 2008 visit, she chose to stage a fashion shoot inside the caverns.

While Crystal Cave and Fantasy Cave (Wilkinson Ave., tel. 441/293-0640, 9:30 a.m.–5:30 p.m. daily May–Sept., 9:30 a.m.–4:30 p.m. Oct.–Apr., by guided tour only) are but two of hundreds of caverns around Harrington Sound and Castle Harbour, they are the largest and the only ones open to the public.

Guided tours are carried out at regular intervals throughout the day; in the winter, when visitor numbers dwindle, you might be lucky enough to get a private viewing. Admission to each cave is $14 for adults and $8 for children ages 5–12 (kids under 5 are free); a combination ticket for both attractions costs $20 for adults, or $10 for children. If you visit just one, Crystal Cave is the most eye-popping and features a greater variety of formations.

Island folklore tells how Crystal Cave was discovered in the early 1900s by two boys playing a game of cricket. When they lost their ball down a hole, they found a subterranean wonderland beneath their feet. A 25-minute tour leads 80 feet down into the earth by way of a steep set of stairs cut into the hard limestone rock. At the bottom, the well-lit series of caverns opens up to expose a sapphire-bottomed lagoon, some 55 feet deep, over which a “floating trail” of pontoon bridges has been erected. Walk across the water, past soaring stalagmites and spear-like stalactites dripping like incessant taps into the pool. The water is incredibly inviting, especially in the torpor of summer, but swimming is not allowed.

A brief “nature walk” leads through an avenue of royal palms and down a red brick path through the estate gardens to Fantasy Cave. Avocado trees, sprawling Indian laurels, fiddlewood forest, and mature cherry groves nearly drown out the traffic at the busy intersection beyond. This cave’s 88 steps wind down to another subterranean wonder, an open area dense with crystalline columns and more stalactites and stalagmites. Narrow walkways allow you to explore various underground nooks and crannies before climbing back to the surface, a 30-minute adventure.

The property has picnic tables under awnings, a café, a gift shop selling (imported) gemstones, rock crystal, and quartz, and some of the nicest pubic bathrooms around.