It’s about four hours north of Mexico City, tucked into a canyon in the mountains of Hidalgo, and the whole place is run by the local community, the ejido of San Cristóbal, who have cared for these springs for generations. The water is heated deep inside the mountain and comes out that impossible milky blue from all the minerals it gathers on the way.

The pools are the showstopper: little terraced basins clinging to the cliff, each one spilling into the next, with the canyon dropping away beneath you. Sink into one with the mountains in front of you and you’ll understand why people make the long drive.

Down on the canyon floor, a turquoise river winds past in a chain of warm, shallow pools and little waterfalls. Follow it to the back of the canyon and you’ll find the grotto itself, where hot water pours from the rock in a cloud of steam, and a narrow tunnel where the spring water runs warm over your feet. It’s like walking into a sauna the earth built.

The secret is timing. I left Mexico City at 4:30 in the morning and had the pools nearly to myself for two blissful hours before the day crowds rolled in. If you can, go midweek, and stay until the late-afternoon light turns the canyon walls gold. It’s rustic and unpolished, and that’s part of its charm: this isn’t a spa, it’s a wild place you get to borrow for a day.

My advice, photographer to friend: shoot the pools from the stairs above, where the terraces stack up into those dreamy layers, and bring a waterproof case for your phone in the river. Wear water shoes, too; the mineral-slick rocks are slippery.

This is a long day, so let us make it an easy one. My agency, Coco Tran Travel, can arrange a private day trip: a driver at your door before dawn, the pools before the crowds, and every bit of timing and logistics handled, so all you have to do is soak.

Inquire about a private day trip

Pair it with a sunrise balloon over Teotihuacán on another morning of your trip. Two early alarms, two of the most beautiful mornings you’ll have in Mexico.