Toniná (9 a.m.–4 p.m. daily, museum closed Mon., US$4) is one of the best Maya archaeology sites that no one seems to know about. Easy to reach from both Palenque  and San Cristóbal  (or as a stop-off between the two) and boasting an excellent museum, this impressive site nevertheless sees only a trickle of tourists.
The first structure you come to on the path from the entrance is Toniná’s unique ball court; at 60 meters long, it’s one of the Maya world’s largest, and has a unique “sunken” construction and is decorated with images of prisoners. Stairs lead up to a massive raised plaza known as the Grand Plaza, also one of the biggest of its kind and dotted with several structures, including a second ball court, this one decorated with images of Toniná’s rulers—and an altar believed to have been used for sacrificing ball-game players (though whether it was the winners or losers remains uncertain).
But by far the most arresting feature of the Grand Plaza is the view it affords of Toniná’s city center, or Acrópolis, a spectacular complex of temples, terraces, and stairways climbing a steep hillside. Nearly 80 vertical meters (260 feet) from top to bottom, the Acrópolis has more vertical gain than any known Maya structure, but is not considered a true pyramid, as it uses the hill to gain height.
The Acrópolis has a total of seven terraces, each with various temples or other structures built on either end. Some visitors take their time reaching the top, visiting the notable structures along the way; others bee-line to the top, then take their time descending. Either way, be aware that the stairs are extremely steep in places, and proper shoes are a must.
On the ground level is a warren of winding passages and tunnels aptly called El Laberinto (The Labyrinth), which connects to El Palacio, one level up. But Toniná’s most famous artifact is a stunning stucco codex known as the Mural de las Cuatro Eras (Mural of the Four Eras) located on the sixth platform. Feathered X-patterns divide the panel into four parts within which are images representing the four eras, or suns, the world was believed to have passed through in Maya cosmology. The images are dark and deathly, including a skeleton holding a human head, an anthropomorphic rat representing a lord of the underworld, and severed human heads representing the passing eras, with feathers protruding from their neck stumps. Parts of the frieze are damaged or destroyed, but those that remain are quite remarkable.
The seventh and final platform is packed with structures, including the Templo del Espejo Humeante (Temple of the Smoking Mirror). The stairs here are incredibly steep, but the view from the summit is breathtaking, albeit somewhat marred by the massive military compound plopped in a sea of farmland.
Definitely leave time to visit the museum (9 a.m.–4 p.m. Tues.–Sun.), which is one of the best at any Maya site. Opened in September 2002, it contains fantastic artifacts and carvings, including figures that were deliberately decapitated (which was probably done when the personage depicted was himself decapitated) and distinctive round obelisks marking important dates.