The Poás Volcano is an active volcano near the town of Poás, Alajuela, Costa Rica. Poas Volcano has two craters. The larger crater is one of the biggest crater in the world. It is 1.6 km (1.0 mi) in diameter and 290 m (951 ft) deep. The biggest known eruption was in 1910.
The area around the volcano is a national park. It is a place where many tourists from Costa Rica and other countries visit. At the bottom of the main crater is a lagoon. The lagoon is an acidic lake with boiling sulfuric gases. The temperature of the lake varies between 20 °C (68 °F) and 50 °C (122 °F). Because of changes in the chemistry of the lake and its temperature, the color of the lake also changes. The second crater has a cold water lake in it. This lake is connected to the nearby river, Rio Angel.