Chiapa de Corzo is the main starting point for boat trips through Cañón del Sumidero. Boat tours (US$10 pp, 9 a.m.–4 p.m. daily) depart from the embarcadero at the end of Calle 5 de Febrero, downhill from the central plaza. Boats leave when they are full (12–16 people); afternoon trips are especially beautiful, but you’ll have less waiting time if you arrive between 9 a.m. and noon, especially in the low season.

The boat takes a little over an hour to reach the dam, with stops and explanations along the way, including at the canyon wall’s highest spot (1,000 m/0.6 mi) and various cave and rock formations, plus a beautiful mist-blown waterfall known as árbol de navidad (Christmas tree) for the lush triangle of moss and vegetation clinging to the wall beneath it.

You can also visit Cañón del Sumidero from above. Catch a trolley (US$7.50 pp, 9 a.m. and 1 p.m. Sat.–Sun., daily during holidays) from Parque Marimba in Tuxtla Gutiérrez for a three-hour trip along the western rim of the canyon, stopping at five miradores (lookout points) for stomach-lurching views of the canyon and river below. You can also drive the route yourself; it’s part of the national park, so there’s an entrance fee of US$2 per car.

Parque Ecoturístico Cañón del Sumidero (tel. 961/602-8500, www.sumidero.com, US$25–29 adult/child) is another of those “eco-parks” where visitors have a series of brief eco-ish encounters and spend the rest of the day reliving it by the pool and over seconds at the $12 buffet. Admission includes the standard boat trip through the canyon (the park is located just before the dam), but there are no return boats until 4:30 p.m.—you’re literally trapped there until then. Most activities, like kayaking, rappelling, and a five-station zip line, cost an additional fee (US$5–15); there are also hiking and biking trails and a small zoo.