Gruta do Carvão, Volcanic cave system in Ponta Delgada, Portugal.
Gruta do Carvão is an underground tunnel system created by ancient lava flows beneath the city. The passages vary in width and height, with walls showing reddish and orange discoloration from oxidation over time.
The cave was first documented in the 16th century when scholars recognized its volcanic origins. Its scientific importance later led to official protection and recognition as a natural monument.
The name refers to the dark charcoal marks visible on the walls as you walk through the passages. These traces reflect the volcanic forces that shaped the cave's appearance and character.
You can only visit the cave with a guide, which ensures you understand the formations properly and move safely through the passages. Wear sturdy shoes because the ground is uneven and some sections are narrow.
Many visitors miss the fact that the conical stalactites were not formed by water but by solidified lava drops instead. These details reveal how volcanic activity shaped every part of the tunnel system.
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