Cozumel Maya Ruins
Good variety of sites for such a small island
Cozumel has 3 Maya ruin sites, which are spread out over almost all the length of the island. However, they can easily be visited during a half day using a rental car. It's unlikely you'll find a tour that includes all 3.
San Gervasio, largest Maya archaeological site on Cozumel was an important political and religious center.