Terceira Island is home to two of the most impressive underground geological monuments in the Azores. Algar do Carvão, a volcanic chimney where you descend 90 meters into the heart of an extinct volcano, and Gruta do Natal, a lava tube nearly 700 meters long. They are located just a few kilometers from each other in the central part of the island, and together they offer one of the most remarkable experiences you can have in the Azores.
In this guide, we explain what you’ll find in each cave, how to plan your visit, and the practical details you should know before you go.
Algar do Carvão: Descending into the Heart of a Volcano
Algar do Carvão is a volcanic cavity formed about 3,200 years ago, considered one of the largest visitable volcanic chimneys in the world. The descent is made via an illuminated staircase that goes down approximately 90 meters to the bottom. As you descend, the landscape changes completely.
The walls are covered by one of the largest collections of silica stalactites known on the planet. Unlike the limestone stalactites found in other caves, these were formed by the precipitation of silica over thousands of years, creating formations that resemble crystal chandeliers hanging from the ceiling.
At the bottom of the cavity, a lagoon of transparent water reflects the natural opening at the top of the volcano. It is the most photogenic moment of the visit, and also the quietest. The interior temperature stays stable at 15°C year-round, making the descent particularly pleasant on hot days.
⚠️ Important note: temporary closure
Algar do Carvão has been temporarily closed since October 2024 for the construction of CAVE (Azorean Volcano-Speleology Center), a new visitor center that will significantly improve reception conditions. Reopening is scheduled for mid-2026. We recommend confirming the current status with the Associação Os Montanheiros before planning your visit.
Gruta do Natal: Walking Inside a Lava Tube
Gruta do Natal is located just a few kilometers from Algar do Carvão and serves as a perfect complement. It is a horizontal lava tube 697 meters long, formed when the outer layer of a lava river solidified while the magma inside continued to flow, leaving behind an underground corridor.
The name comes from a tradition started by the Associação Os Montanheiros: the cave was first opened to the public on Christmas Day 1969, with a mass celebrated inside. The tradition continues.
Unlike the vertical experience of Algar do Carvão, here you walk through a relatively flat corridor for about 30 minutes. The textured walls show the different cooling phases of the lava: pahoehoe formations (ropey lava), lava stalactites, marks from different magma flow levels, and solidified gas bubbles. The lighting installed along the path highlights these geological details.
How to get to the caves
Both caves are located in the central area of Terceira Island, in the Mistérios Negros area. Starting from Angra do Heroísmo, the drive takes between 20 to 25 minutes via the regional road, passing through typical Azorean pastures and rural landscapes. From Praia da Vitória, the time is similar.
There is no regular public transport to the caves. The most practical way to get there is by rental car, which also allows you to combine the visit with other spots in the central area, such as Furnas do Enxofre or the Mistérios Negros trail (PR1 TER), which passes right by Gruta do Natal.
Checklist for your visit
- Time needed: Allow 2 to 3 hours to visit both caves at a relaxed pace
- Clothing: Bring a jacket, as the temperature inside is around 15°C, even in summer
- Footwear: Sneakers or boots with non-slip soles (mandatory)
- Photography: You can take photos, but avoid flash in areas with sensitive formations
- Schedules: Always confirm opening hours before you go, especially outside of peak season. Both caves close during part of the week in winter
Frequently asked questions
Can I visit Algar do Carvão in 2026? It depends on the phase of the construction. Algar do Carvão has been closed since October 2024 for the construction of the new CAVE visitor center, with reopening scheduled for mid-2026. Check with the Montanheiros.
What is the difference between Algar do Carvão and Gruta do Natal? Algar do Carvão is a vertical volcanic chimney where you descend 90 meters via stairs to an underground lagoon. Gruta do Natal is a horizontal lava tube nearly 700 meters long, explored on foot. They are complementary experiences.
Is it worth buying the combined ticket? Yes. The combined ticket costs €15, compared to €19 if bought separately (€10 + €9). Besides the savings, the caves are just a few minutes away from each other.
Are the caves accessible for children? Yes, children can visit both caves. Algar do Carvão requires some ability to climb steep stairs. In Gruta do Natal, helmets are mandatory and the ground is uneven.
Do I need to book in advance? No. Tickets are sold on-site, with no need for prior reservation.
