Barely an hour from the capital, Poás volcano rises to 2,700m. It is made up of three main craters. The largest, 1.5 km in diameter, is one of the biggest in the world, reaching a depth of 300m. The crater holds an acid lake with a pH below 1, making it one of the most acidic lakes on the planet. Sulphurous fumaroles are the volcano's main emissions, some rising hundreds of metres into the air. Two other craters lie within the national park. Laguna del Boto is filled with clear water and last erupted 7,500 years ago; it is easily accessible and observed. The third, Von Frantzius (named after the German scientist who first observed it in 1861), is difficult to reach. This stratovolcano's activity dates back 11 million years, but it was in January 1910 that a massive explosion sent a column of smoke over 8,000m into the sky above the cone, scattering ash and rock for kilometres around. Since then, the volcano has experienced frequent phreatic eruptions. Access to the volcano is straightforward, and the road from Alajuela is strikingly beautiful. It runs alongside the distinctive crops grown in volcanic regions — strawberries, cabbages, coffee and flowers are cultivated here year-round. A wide path leads to the main crater. Another trail allows you to admire the second crater, El Boto. From there, an easy short walk crosses the high-altitude tropical forest that makes up most of the national park's vegetation. You will also see striking specimens of tree ferns and Gunnera manicata (the poor man's umbrella plant). The main residents here are hummingbirds, trogons — including a few quetzals — toucans, and a handful of mammals such as bats, weasels and marmots. That said, it is not the wildlife that makes the trip worthwhile, but the volcano itself.
