On the slopes of Turrialba Volcano lies Costa Rica's most significant and only true archaeological site. Records mentioning the ruins go back to the mid-1800s, but systematic investigations didn't begin until 1968, when a local landowner out walking her dogs discovered what she thought was a tomb. Archaeologists began excavating the site and unearthed the base wall of a chief's house in what eventually turned out to be the ruins of a large community (around 10,000 inhabitants) covering 49 acres, 10 of which have been excavated. The city was abandoned in AD 1400, probably because of disease or war. Guided tours (about two hours) in Spanish or English make the stones come alive, with knowledgeable guides from the U-Suré Guide Association (the name is the indigenous word for house). Starting from the round, thatch-roof reception center, they'll take you through the rain forest to a lookout from which you can see the layout of the excavated circular buildings. Only the raised foundations
survive, since the conical houses themselves were built of wood. As you descend into the ruins, notice the well-engineered surface and covered aqueducts leading to a trough of drinking water, which still functions today. Next you'll pass the end of an impressive 8-km (5-mile) paved walkway used to transport the massive building stones; the abstract patterns carved on the stones continue to baffle archaeologists, but some clearly depict jaguars, which were revered as deities. Excavations in 2013 began to unearth an elaborate system of agricultural terraces.
Guayabo has been recognized by the American Society of Civil Engineers as a feat of Latin American civil engineering second only to Machu Picchu. The hillside jungle is captivating, and the trip is further enhanced by bird-watching possibilities: 200 species have been recorded. Facilities at Guayabo are still minimal: there's a souvenir hut opposite the entrance, a pleasant picnic area, and modern restrooms in a replica of a thatched indigenous hut. The access route from the east via Santa Teresita (Lajas) has some rough spots, but you can make it in any car. The alternative Santa Cruz route is a little rougher, but still driveable in a regular car, unless the road is wet—in which case you may need a four-wheel-drive vehicle to get here.