Fumarole (steam) rising from the Poás crater.

The Poás Volcano is an active stratovolcano in central Costa Rica.
It has erupted 39 times since 1828. There are two crater lakes near
the summit of the Poás Volcano. This lake pictured above is the northern
lake known as the Laguna Caliente ("hot lagoon") and is located at a height
of 2,300 m in a crater approximately 1.7 km wide and 290–300 m deep. It is
one of the world's most acidic lakes. The acidity varies after rain and
changes in volcanic activity, sometimes reaching a pH of almost 0;
consequently, it supports little or no aquatic life. The bottom
of this lake is covered with a layer of liquid sulphur. Acid
gases create acid rain and acid fog, causing damage to
surrounding ecosystems and often irritation of eyes and lungs.