This is the largest and most important archaeological site in the country. Although Guayabo is not nearly as breathtaking as Mayan and Aztec archaeological sites (don't expect pyramids), excavations have unearthed sophisticated infrastructure and mysterious petroglyphs. Polychromatic pottery and gold artifacts found here are also exhibited at the Museo Nacional in San José.
The most impressive find at Guayabo is the aqueduct system, which may have served more than 20,000 people in AD 800, the height of the city's prominence. It uses enormous stones hauled in from far-off Río Reventazón along an 8km (5mi)road that's in pretty good shape (by Costa Rican standards). The extra effort was worth it - the cisterns still work and (theoretically) potable water remains available onsite, which you can enjoy among various unearthed structures and unexcavated mounds.
The site, which may have been occupied as early as 1000 BC, was mysteriously abandoned by AD 1400 - the Spanish conquistadors, explorers and settlers left no record of having found the ruins. Though underfunded archaeologists continue to hypothesize about Guayabo's significance, most believe it was an important cultural, religious and political center.
