San Cristóbal [1] has a vibrant nightlife [2], mostly in the form of small bars and cafés where you can knock back a beer or mixed drink while listening to live acoustic, rock, or reggae music. More and more spots are staying open into the wee hours, but the majority still close at midnight—to be safe, plan on getting your groove going early.
For an even mellower outing, try catching a play, documentary, or Hollywood movie at one of the local theaters [3].
Links:
[1] http://www.moon.com/destinations/chiapas/san-cristobal-de-las-casas
[2] http://www.moon.com/destinations/chiapas/san-cristobal-de-las-casas/entertainment-and-events/nightlife
[3] http://www.moon.com/destinations/chiapas/san-cristobal-de-las-casas/entertainment-and-events/the-arts