Guayabo National Monument

  Guayabo National Monument is located 19 kms. (12 miles) north of Turrialba volcano and is Costa Rica's most important archaeological site. In 1968, a city was unearthed accidentally on this site, a city where it is reported that some 20,000 inhabitants once lived on an area of around 49 acres. The city was abandoned in the year 1400 AD due to any number of reasons ranging from sickness to starvation, etc. Or perhaps the site stopped being used for whatever purpose it was intended, and was thus abandoned.
  The area is covered in rain forest with a central clearing which allegedly holds the foundations of the houses of the chiefs of the former city. These foundations are fairly circular in shape, and could have been used for another purpose altogether. There is an aqueduct which functions to this day, amazing since nobody inhabited the area for at least five hundred years! There is also a five mile paved road where it is said that the people came in from the woods, and whereon massive building stones were once transported. There are carved abstract patterns on stones which baffle archaeologists. Some depict jaguars which were revered by Indians as deities.

Bibliography
Fodor's Costa Rica, Belize, Guatemala, Editor: Carolyn Price,
Fodor's Travel Publications, Random House, New York, 1993.