Chichen Itza

Overview
Chichen Itza (/tʃiːˈtʃɛn iːˈtsɑː/, Spanish: Chichén Itzá, from Yucatec Maya: Chi'ch'èen Ìitsha' "at the mouth of the well of the Itza") was a large pre-Columbian city built by the Maya civilization. The archaeological site is located in the municipality of Tinum, in the Mexican state of Yucatán.

Chichen Itza was a major focal point in the northern Maya lowlands from the Late Classic (c. AD 600–900) through the Terminal Classic (c.AD 800–900) and into the early portion of the Early Postclassic period (c. AD 900–1200). The site exhibits a multitude of architectural styles, reminiscent of styles seen in central Mexico and of the Puuc and Chenes styles of the northern Maya lowlands. The presence of central Mexican styles was once thought to have been representative of direct migration or even conquest from central Mexico, but most contemporary interpretations view the presence of these non-Maya styles more as the result of cultural diffusion.

Via Wikipedia

Benefits apply to every town in the Civ not just the town it is built in

 * Increases Arrow Tower and Cannon Tower hitpoints by 15%
 * Adds a hit-point regeneration rate to all structures of 2 HP per second.
 * Decreases the amount of towns your civ needs to win via Conquest Victory from 75% to 50%