The mayan ruins of Coba in the Yucatan Peninsula, are the biggest of the area, including the biggest built by the mayan civilization. It's located 40 km away from Tulum and you can arrive from Cancun by taking the ADO or by book a tour with your customer service representative at your hotel.
One of the main attractions o Coba is "Nohoch Mul", the tallest piramid in the Yucatan Peninsula, it raises 42 m. Usually you can climb on it as is the onlye one left that you can climb, but from time to time it's been repaired. If you can manage to climb it you will be able to see the surrounding jungle. also there is a ball game court where ancient mayas used to play for honoring the gods.
It doesn't look as spectacular as Chichen Itza, but its worth the trip as you can actually intereact with real mayan people that kept their culture and customs and transport you into time.
Another important tip is that you can rent bicycles.