incón de la Vieja (1,895 meters), 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 (1,916 meters) the tallest and most easterly. Its crater harbors a forest-rimmed lake popular with quetzals, linnets, and tapirs.

The main crater--Von Seebach, sometimes called the Rincón de la Vieja crater--still steams. Icy Lake Los Jilgueros lies between the two craters. The last serious eruption was in 1983. Rincón, however, spewed boiling mud and acid gases on 8 May 1991, causing destructive lahores (ash-mud flows). 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 name Rincon de la Vieja is translated as "Old Woman's Nook" and refers to the legend of a young girl whose lover was thrown into the volcano by her father, after which she became a recluse with healing powers .