I visited the "Algar do Carvao" on octobre the 16th,2024.

The Azores are home to no fewer than around 1700 volcanoes! Algar de Carvão is one of them. However, this volcano is no longer active. Today it is a 90 meter deep cave that was created thousands of years ago by volcanic activity. It is a volcanic vent that you enter. The upper part is covered in greenery due to the incidence of light and  humidity. You descend up to 90 meters underground, where there is a small but up to 15 meter deep lake. Several platforms offer a view of various rock formations. The most beautiful thing, however, is the view outside. The sun shines through the large hole in the ceiling and ensures that a large edge of the chimney is lush with bushes, mosses, lichens and ferns. Some endemic species are also said to grow in the volcanic vent. 
Algar de Carvão is located just 12 kilometers from the capital of Terceira, Angra do Heroísmo. You can buy a combination ticket for the Algar do Carvao and the Gruta Natal (pretty boring) for €15.

I for my part wasnt very impressed and after around 20 minutes I ended my visit there. I didnt see any endemic life form nor any life form at all inside the Algar apart from some fellow tourists.

I then left the Algar do Carvao and when on the way back to the parking lots I spotted a hiking trail on the right side.It is not an official one,but a quite good one. I followed the easy path up and enjoyed the spectacular view that kept opening up to me in the sea of ​​green. I hoped the path would take me along the edge of the chimney, but it went sideways. Nevertheless, the approximately 40 minute tour up and down again was much more interesting than the Algar do Carvao itself.

I for my part didnt see any OUV in the Algar do Carvao,but other mid-atlantic ridge sites may offer more.

The opening times are strange, so it's better to find out more about them before visiting. Normal clothing is sufficient, but I would recommend good shoes, as the unofficial hiking trail to the top is relatively easy, but can be a little slippery after rain .