A Mayan city from the classic epoch on the Yucatan peninsula, south of Mérida.
You should visit the site in the morning and then go to one of the numerous cenotes in the area to cool off during the afternoon as it's really hot in the area!
Uxmal is truly impressive and very well preserved.
The placement of the buildings is dictated by astronomy and if you use a local guide during your tour you'll have the added benefit of finding out about what all the symbols on the different buildings mean. This city is considered to represent the apogee of Mayan art.