Gruta do Carvão, also known as the Grotto of Coal, is an ancient lava tube located on the island of São Miguel in the Azores. It's a cool spot with stalactites, stalagmites, and other speleological structures along its 1,650-meter length. Gaspar Frutuoso, a 16th-century chronicler, mentioned it in his writings, adding to its historical charm. The grotto was designated as a Regional Natural Monument in 2005 due to its scientific, educational, and touristic value. So, if you're ever in Ponta Delgada, swing by this natural wonder for a unique underground adventure!