San Cristóbal is the base for highland Chiapas, and almost everything is a day trip from here.
The Sumidero canyon, an hour away past Chiapa de Corzo, is a thousand-metre gorge with boats running the Grijalva between its walls — crocodiles, spider monkeys, and a waterfall over a mossy cliff shaped like a Christmas tree.
San Juan Chamula and Zinacantán, both within half an hour, are Tzotzil Maya villages with their own governance. Chamula's church is the reason people go: no priest, a floor covered in pine needles, thousands of candles, Coca-Cola and posh used in healing ceremonies, and photography strictly forbidden inside — the prohibition is enforced by the village and taking a camera out has consequences. Go with a guide who explains the rules before you arrive.
Further out: Palenque with the waterfalls at Agua Azul and Misol-Ha, the lakes at Montebello on the Guatemalan border, and the long day to Yaxchilán and Bonampak on the Usumacinta.
San Cristóbal is also a political town — the Zapatista uprising began here on New Year's Day 1994 — and that history is visible in the murals, the cooperatives and the bookshops. Treat the politics as the living thing it is rather than a souvenir.