Twelve kilometers southeast of San Andrés, in the eponymous village, a 250-step staircase leads down to the absolutely spectacular Salto de Eyipantla, a 50m-high, 40m-wide waterfall. Scenes from the movie Apocalypto were filmed here. To avoid the steps (and a soaking at the base) there's a mirador (lookout) at the top of the falls, which is free.
Frequent TLT buses (M$15) and taxis (shared/whole M$30/100) run from San Andrés, leaving from the corner of Cabada and 5 de Mayo, near the market. If driving, follow Hwy 180 east for 4km to Sihuapan, then turn right to Eyipantla.