Chacchoben is the most practical Maya site to pair with Bacalar, especially if you have a car or arrange a tour. The ruins sit north of town, with temple platforms, forest, and enough scale to make the detour worthwhile.
It does not have the fame of Tulum or Chichén Itzá, which is part of the appeal. Go early for cooler weather and bring water; shade helps, but the heat still catches up.