Catemaco sits on a volcanic crater lake in Los Tuxtlas, the northernmost tropical rainforest in the Americas and a biosphere reserve. The combination — rainforest at the latitude of the Bahamas — is why the biology here is strange and why the forest is worth more than the lake.
Boats leave from the malecón for the islands: Isla de los Monos, where a colony of Thai macaques brought for research in the 1970s now lives free; Isla de las Garzas with its herons; and the shore springs. A basic circuit takes about an hour.
The reserves along the north shore run guided forest walks with mineral springs, mud baths and temazcal. Inland, the waterfalls at Salto de Eyipantla are a short drive, and the biological station at Los Tuxtlas can be visited by arrangement.
Catemaco is also Mexico's brujería town, and the first Friday in March brings a national gathering of curanderos. Some of it is serious and traditional, a good deal of it is sold to visitors, and the difference is not obvious from outside. Treat it with the same scepticism you would bring anywhere.