Algar do Carvão, probably the only known place in the world where you can walk inside the cone of a volcano. There was an initial explosion some three thousand two hundred years ago, and then two thousand years ago another eruption at the same site spewed molten lava inside the mountain. When the lava drained, it left chambers whose rock walls were as varied in colors of bronzes and golds as the cloak of the lover in the Gustav Klimt painting The Kiss.
