Close to Orange Walk Town, Cuello (kway-yo) is one of the earliest-known settled communities in the Maya world, probably dating back to around 2400 BC, although there's not much left to show for it. Archaeologists have found plenty here, but only Structure 350, a nine-tiered pyramid, is of much interest to the non-expert. The pyramid was constructed around AD 200 to AD 300, but its lower levels date from before 2000 BC.
The site is on private property owned by Cuello Distillery, 4 miles west of Orange Walk (take San Antonio Rd out of town). It is not really open to the public, although the distillery usually allows access if you turn up during office hours. It's a good idea to call and make advance arrangements. A taxi to Cuello from Orange Walk costs about BZ$25, round trip.