Poás Volcano National Park

Poas rises to about 2,700 metres, and its summit holds two crater lakes. Laguna Caliente, the northern lake, sits in the main active crater, which SINAC's park profile gives as roughly 1.3 kilometres across and about 300 metres deep. Wikipedia calls it one of the world's most acidic lakes, with a pH that can fall close to zero and a layer of liquid sulfur on its bottom. Its acidity shifts with rainfall and volcanic activity.

The southern lake, Lake Botos, fills an inactive crater whose last eruption is dated to around 7500 BC. Its water is cold and clear and the crater is ringed by cloud forest. A third crater, Von Frantzius, is also inactive and is reached by trails when conditions allow.

Poas has erupted about 40 times since 1828 according to Wikipedia. A major eruption cycle ran from 1953 to 1956, and eruptions often include geyser-like ejections of lake water. In January 2009 an earthquake near Poas caused heavy damage in the Cinchona area. In April 2017 a series of explosions sent ash and incandescent rock across a wide area and damaged park buildings, after which the park was closed for a long period and reopened with restrictions and a safety perimeter.

The volcano is monitored for gas emissions, and in 2022 the International Union of Geological Sciences included Poas among its first 100 geological heritage sites. Because volcanic conditions change, access to the crater viewpoint can be limited or suspended, and the national authorities are the reliable source on current arrangements.

The park covers about 65 square kilometres and was established on 25 January 1971. It is managed by SINAC and sits in the Central Conservation Area. Vegetation includes the Poas magnolia, and Wikipedia lists the resplendent quetzal, black guan, clay-colored robin and several hummingbirds, tanagers and toucan species among its birds.

Mammals are not abundant but include coyotes, long-tailed weasels, Dice's cottontail rabbits, striped hog-nosed skunks, Deppe's squirrels and nine-banded armadillos. Acid gas from the main crater damages vegetation nearby, which is visible as bare or stunted patches in satellite imagery.

The volcano is within easy reach of the capital, and it is commonly combined with highland stops such as waterfall gardens and coffee farms. Weather matters: the crater is often hidden by cloud by midday, so early starts are typical. A private guided visit lets a driver handle the mountain road and a guide explain the volcanic features if the viewpoint is open on the day.