Poás Volcano with Laguna Caliente, Parque Nacional Volcán Poás, Costa Rica
The lake in the crater is one of the world's most acidic lakes with a pH of almost 0 and a temperature of 40° C.
The volcano is 2574m high, has a diameter of 1320m and depth of 300m. It has erupted 39 times since 1828 and is still active.
On a clear day you are supposed to see the carribean and pacific coast from here.