Temazcals are steam baths with ancient native traditions.  
Temporarilily
read this, while I sweat out some more research.
Tourism in Catemaco, Los Tuxtlas, Veracruz, Mexico

Temazcals
Nanciyaga
the prettiest sweat dome, and also the most public
more information
Playa Azul Spa and Condo Hotel
A temascal in a jungle garden setting.  
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Ecoparque
a "homemade" slew of sweat lodges and massages, a few blocks from downtown
website
La Finca Resort Hotel & Spa
while being built, we thought a flying saucer had landed.
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Benito temascalli
past Playa Azul
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