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. ...