Labná (8 a.m.–5 p.m., free admission) is for many people the best of the four smaller ruins on teh Puuc Route [1].
At least 60 chultunes (underground cisterns) have been found in the Labná area, suggesting a population of about 3,000 residents at its peak, around A.D. 750–1000.
Links:
[1] http://www.moon.com/destinations/cancun-the-yucatan/the-state-yucatan/the-puuc-route