Cave Algar do Karvan is an ancient lava tube, or so-called volcanic crater on the island of Terceira. The cave is located in the Central part of the island in the district of Porto-Judau in the municipality of Angra do Heroísmo.

The word "Algar" in Portuguese language means a natural depression in the earth, which, unlike most caves, located vertically, like a well. The word in Portuguese comes from the Arabic language, its original meaning was "borderline". "Karvan" translated from Portuguese as "coal", but in the cave of coal no, it's just the emphasis on the fact that the cave is dark.

The island of Terceira is formed by four volcanoes Pico Alto, Santa Barbara, Gillermo Moniz and the Cinco Picos along basaltic fissure zone that divides the island in half and stretches from Northwest to Southeast. Cave Algar do Karvan directly adjacent to the Caldera of Gilarmi Moniz, and is situated at an altitude of 550 meters above the sea level. You can go down to about 100 meters, where there is a lake with crystal clear water.

The cave is known for its unique mineralogical characteristics of stalactites and stalagmites. They are considered the most beautiful on the Azores archipelago. The area of the cave – 40.5 ha. Due to its geological characteristics, this cave is recognized as the "regional natural monument".

The existence of the cave has been known for a long time, but due to the fact that the inside is very dark and it was dangerous to go down, the cave was insufficiently investigated. In January 1893 in the cave descended first expedition. Re-study of the cave was investigated already in the twentieth century, in 1934. After this expedition had drawn a map of the cave.