Mayapan is a compact Maya archaeological site southeast of Merida, once the political capital of the Yucatan Peninsula. It is smaller than Chichen Itza or Uxmal, but the ruins are well preserved and the site is easier to take in without a full-day commitment.
One advantage here is rare in the Yucatan's big-name ruins: some pyramids can still be climbed. Bring water, as services are limited.