There are over 200 volcanic formations in Costa Rica, but not all are active. Some of the most well-known volcanoes in Costa Rica include Arenal, Irazú, and Poás. Arenal is an active stratovolcano in the province of Alajuela, while Irazú is an active stratovolcano in Cartago. Poás is an active stratovolcano located in the province of Alajuela, and it is known for its large, active crater lake.