Inside the incredible 330ft-long volcanic cavern that'ssmothered in lush vegetation and home to an underground lake

The Algar do Carvão is a volcanic cavern located on Terceira, one of the largest islands in the Azores 

The top of the vent is surrounded by green vegetation and there is a manmade staircase inside for visitors

At the bottom of the cave is a rain-fed lake that can swell to a depth of 50ft when it's particularly wet