Overview
The two eyes are connected by a 400-metre passage, and the wider system was surveyed as part of Sac Actun after divers linked them in 2018 — making the combined system some 370 kilometres long. Guided cavern dives run through the illuminated sections; the bat cave and the barbie line are the standard routes. Snorkellers stay in the open pools, where the halocline and the light shafts are both visible without any training.
Highlights
Go with a guide for the cavern; the open pools need only a mask and a life jacket, which is included. The water is 24 to 25 degrees year-round, which feels cold after an hour, so a shorty wetsuit is worth renting. Bring cash and get there early — the parking fills and access is by a rough track from the highway.