Located to the southeast of Arenal at 1.100 meters. It is a volcanic truncated cone. At the summit it has an exploded crater of 500 meters in diameter, where there is an oval shaped lagoon, 250 meters long and 150 meters wide. The extension of this volcano is 10 Km2. Chato Volcano, sometimes called “Cerro Chato”, is an inactive volcano in north-western Costa Rica north-west of San José, in the province of Alajuela, canton of San Carlos, and district of La Fortuna. It is southeast of the nearby Arenal Volcano. It is believed Cerro Chato first erupted 38,000 years ago during the Pleistocene period and last erupted about 3,500 years ago. One of the lava flows is now the route for La Fortuna Waterfall. The hill has two peaks, named Chatito (little Chato) and Espina (Thorn). A crater about 500 metres (1,600 ft) wide is filled with green water, making the Laguna Cerro Chato. It is possible to hike the Cerro Chato up to and inside the crater, but it is considered a difficult hike and only recommended for hikers of good physical condition. There are two possible routes, one beginning from near the La Fortuna Waterfall and one from The Arenal Observatory Lodge & Spa on the west slope. It is possible to ascend on one side and descend on the other, but this makes for a longer hike. When it rains, the path becomes muddy and can make it even more treacherous, especially when descending into the crater itself. Due to certain minerals in the water, swimming is not recommended, but many locals swim in it regardless. The water is fairly cool.The hike to the crater is decently long (taking approximately 4 hours with a guide) and very steep. It begins in lower farmlands with few trees, but quickly ascends to a much steeper climb through the thick rain forest. The ascent from the Observatory Lodge has a good view over the town of La Fortuna.