Turrialba National Park and Guayabo Monument-Turrialba, (3,349 m) the southeast-most of Costa Rica's Holocene volcanoes, is a large vegetation-covered strato-volcano located to the northeast of Irazu volcano. Turrialba has been quiescent since a series of explosive eruptions in the 19th century that were sometimes accompanied by pyroclastic flows. Fumarolic activity continues at the summit craters. It is possible to descend to the crater bottom. Guayabo Monument is one of the most important archeologic areas and the biggest in size that has been discovered in the country. ( http://adventure-costarica.com/travel/costa_rica_national_parks/turrialba_volcano.htm)