Chac Mool

Chac Mool has two entrances and two very different characters. Kukulkan is the photogenic one — a wide shaft of light falling into a chamber full of formations. Little Brother is tighter and more decorated.

Both lines cross haloclines, where fresh and salt water meet and your vision blurs like heat haze until you pass through.

The air dome partway round is the moment people remember: you surface inside a sealed chamber in complete darkness, take your regulator out, and hear your own voice underground.