Well there is Chichen Itza, Museo Maya de Cancun, El Ray ruins and much much more. There are easy tours to take that will get you to see a few in a whole day to maximize your sun exposure time. From Cancun it's about 75-100 minutes to most of the ruins and historical sites. When we were last in Tulum 2 years ago we got to see 4 different ruins/historical sites and swim in freshwater sinkhole that was rather intricate. There are scuba tours of some of them. If you haven't booked your hotels yet and don't want the typical tourist resort experience take a look at Tulum. We stayed at Be Tulum and can't recommend it enough. That staff, rooms and restaurant are great. I rarely will have more than a quick breakfast at a hotel restaurant but when I can order fresh whole fish or lobster on a grill that is on the beach I will stay for dinner.