Oxtankah (8 a.m.–5 p.m. daily, US$3.50) is a small archaeological site whose name means Between Branches, so called by early archaeologists after the many trees growing amid, and on top of, the structures.
Relatively little is known about Oxtankah—including its true name—but it probably arose during the Classic era, between A.D. 300 and 600, and was dedicated primarily to trade and salt production. At its height, the city extended to the shores of Chetumal Bay and included the island of Tamalcab.
Oxtankah’s principal structures were constructed in this period, suggesting it was a fairly robust city, but it was apparently abandoned around A.D. 600, for unknown reasons. The city was reoccupied by Maya settlers almost a thousand years later, in the 14th or 15th century, during which time a number of structures were expanded or enhanced. It was still occupied, mostly by modest earthen homes, when the first Spanish explorers arrived.
Some researchers have suggested the infamous Spaniard castaway Gonzalo Guerrero lived here; Guerrero was shipwrecked in this area in 1511 and adopted Maya ways, even marrying a chieftain’s daughter—perhaps most significantly, their children are considered the New World’s first mestizos, or mixed-race people.
In 1531, conquistador Alonso de Avila attempted to found a colonial city on the site, but he was driven out after two years of bitter conflict with local residents. He did manage to have a Franciscan chapel built, the skeleton of which remains, including an impressive eight-meter-tall (24-foot) arch.
Today, most of the excavated structures in Oxtankah surround two plazas: Abejas (Bees) plaza, the city’s main ceremonial and elite residential center, and the somewhat smaller Columnas (Columns) plaza, whose large palace probably served an administrative function.
Architecturally, the structures are more closely related to those of the Petén region  (present-day Guatemala) than to Yucatecan ones, suggesting a close relationship with that area. There’s a small museum on-site; signage is in Spanish only.
Oxtankah is located seven kilometers (4 miles) north of Calderitas , about one kilometer (0.5 mile) off the bayside road. There’s no public transportation to the site; a cab from Calderitas costs US$2.50 each way; one from Chetumal  will run about US$15 round-trip, including wait time.