Achada das Furnas, the Azores Achada das Furnas on the island of San Miguel is home to the 'caldeiras', depressions formed by volcano explosions, in the middle of which you'll see bubbling hot mud. Martin Siepmann/ age fotostock
On the island of Terceira, the volcano Algar do Carvão conceals a shaft 147 ft deep, a hearth of vegetation tapered with wet moss, where it can be accessed through a tunnel. Places to see on the island of Terceira are the caldera of Guilherme Moniz (a crater of 2 miles in diameter in the centre of the island), the furnas do Enxofre and the Biscoitos (lava forms and natural pools).
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