Rincón de la Vieja, an active volcano in a period of relative calm, is the largest of five volcanoes that make up the Cordillera de Guanacaste. It is composed of nine separate but contiguous volcanic craters, with dormant Santa María the tallest and most easterly. Its crater harbors a forest-rimmed lake popular with quetzals, linnets, and tapirs. The main crater still steams. Icy Lake Los Jilgueros lies between the two craters. The slopes still bear reminders of the destructive force of the acid cloud that burnt away much of the vegetation on the southeastern slope.
The attractions are protected by CostaRica in the 14,083-hectare Parque Nacional Volcán Rincón de la Vieja, the diverse conditions foster a panoply of wildlife species. More than 300 species of birds include quetzals, toucanets, the elegant trogon, eagles, three-wattled bellbirds, and the curassow. Mammals include cougars, howler, spider, and white-faced monkeys, kinkajous, sloths, tapirs, tayras, and even jaguars.
The lower slopes can be explored along relatively easy trails that begin at the park headquarters. The Sendero Encantago links with a 12-km trail that continues to Las Pailas, 50 hectares of bubbling mud volcanoes, boiling thermal waters, vapor geysers, and the so-called Hornillas geyser of sulfur dioxide and hydrogen sulfide. The mud has minerals and medicinal properties used in cosmetology.