The point of staying in Chetumal is what is around it. The Maya ruins of Kohunlich, with its vast stucco masks of the sun god, and Dzibanché are both within an hour or so; the Río Bec sites — Becán behind its dry moat, Chicanná with a doorway built as a monster's mouth — and Calakmul itself lie west along Highway 186. Closer to the city, the Laguna Bacalar — the famous "lagoon of seven colours" — is a 40-minute drive north and easily the most popular escape from Chetumal.
Across the border, Belize opens up: Corozal Town is a 20-minute taxi ride, San Pedro on Ambergris Caye an hour by water taxi from Chetumal's marina. Cheap and easy if you have the passport stamp room.