Rancho Nuevo (9 a.m.–4:30 p.m. daily, US$1) is one of many cave systems, or grutas, piercing the mountains of Chiapas [1], and certainly one of the easiest to visit, with electric lighting and a cement pathway wide enough to drive a small car on.
That’s not to say it’s unimpressive—the path winds more than a half mile underground, with a roof that’s over 22 meters (75 feet) high in places, and covered in dangling stalactites. Outside are a dozen open-air eateries, a playground, even horseback riding, and weekends can get quite busy with local families.
In 1994, Zapatista rebels used the caves to launch attacks against an adjoining military base; as a result, Rancho Nuevo is controlled by the army—those blasts you hear are from target practice—and exploring beyond the designated areas is strictly forbidden.
Ocosingo [2]-bound combis or pickups can drop you at the Rancho Nuevo turnoff (US$1, 20 mins); from there it’s a 500-meter walk to the visitor area.
Links:
[1] http://www.moon.com/destinations/chiapas
[2] http://www.moon.com/destinations/chiapas/palenque/ocosingo