Furna do Enxofre on Graciosa: the cave in the Caldeira, the tower stairs and walking the rim

If you come to Graciosa for one sight, it is this one: a lava cave under the floor of the island's crater, reached by a stone tower and 183 steps. The decisions are small but they matter. Should you drive in or walk the rim first, when is the visitor centre open, and is the descent right for everyone in your group?

The Caldeira is the crater at the top of the volcano in Graciosa's southeast corner. It is an oval hollow about 1.6 by 0.8 kilometres, left when the summit collapsed after large explosive eruptions roughly 12,200 years ago. The rim reaches 405 metres, the highest ground on the island.

The Furna do Enxofre sits under the crater floor. The regional tourism board gives it as 194 metres long and about 50 metres high at the centre, and describes the roof as the largest volcanic dome in Europe. At the bottom there is a pond of cold water around 11 metres deep and a fumarole where muddy water bubbles and gas escapes from the floor. The name means "sulphur cave".

Prince Albert I of Monaco visited in 1879 and was one of the first to climb down on a rope ladder. The stone access tower was finished in 1939, and the visitor centre at the top opened in 2010.

You enter through the visitor centre, which has an exhibition on the lower floor and the reception and cave entrance on the upper floor. From there a tower 37 metres high takes you down a spiral staircase of 183 steps to the cave floor.

What to expect on the stairs:

• You come back up the same 183 steps. For anyone with bad knees or heart trouble, the climb out is the harder half.
• Wear shoes with grip rather than sandals; it is a long spiral in both directions.
• Children under 12 have to be with an adult.
• The gas readings decide whether you get in at all, which is the next thing to understand.

Carbon dioxide seeps out of the cave floor. The gas is heavier than air and collects low down, and in still weather the concentration can rise above safe limits for people. The site is monitored continuously, and screens in the visitor centre show the current gas values from inside the cave.

This is not a hypothetical risk. In July 2007 the cave was closed after the regional volcanology centre measured carbon dioxide close to 10 per cent inside, and the scientists said it would stay shut until the weather changed. So if you arrive and the staff tell you the cave floor is closed, that is the reason, and there is no way around it. The management also reserves the right to close the centre in bad weather.

The visitor centre works to a seasonal timetable. The pattern has been a day split by a lunch break, open every day in summer and with closing days (Sundays and Mondays in the last published winter schedule) from November to April. The current times are published by the regional natural parks service and have changed between years, so check before you go. Ring the centre on +351 295 714 009 if your day on the island depends on it.

Ticket prices on the regional environment site in 2025:

• Adults (15 to 64): 5 euros
• Juniors (7 to 14) and seniors (65 and over): 2 euros
• Children up to 6: free
• Family ticket, two adults with children up to 14: 10 euros
• Azores residents: free with a Citizen Card

Those are 2025 figures; confirm on arrival.

The visitor centre's own directions start from the main square in Santa Cruz da Graciosa. Drive 3 kilometres to the centre of Guadalupe, turn left towards Pedras Brancas for 3.8 kilometres, then follow the signs to the Caldeira along the Canada Longa. The last stretch passes through a road tunnel of about 200 metres in the crater wall and drops onto the crater floor, where the visitor centre is.

A hire car or a taxi from Santa Cruz is the practical way in; the route has several turns, so load it on your phone before you leave the town.

Driving in gets you to the cave in a few minutes. Walking the rim shows you what the cave sits inside, and on a clear day you can see across to the other islands of the central group.

The official route is PRC05GRA, "Subida ao Cume", a circular walk of 9.7 kilometres graded hard, with about three and a half hours on foot. It starts in front of the church of Nossa Senhora da Luz in the village of Luz, climbs to the ridge and goes round it, passing the island's highest point at 405 metres. On the way it passes three caves: the Furna da Maria Encantada, the Furna do Abel and the Furna do Enxofre itself. Check the route and current condition on the official Azores trails site before you set out.

Before you commit:

• Three and a half hours is walking time. Add stops, and the cave visit if you want it the same day.
• The inner slopes are covered in Japanese cedar, the biggest stand of forest on Graciosa. In low cloud you see trees and little else, so pick a clear morning.
• If you want the cave as well, time the walk so you reach the visitor centre inside its opening hours.

If you do not have three and a half hours, the Furna da Maria Encantada gives you most of the view for a fraction of the effort. It is a lava tube 56.5 metres long through the crater wall, easy to walk through, and it opens on the inner side of the crater with a view over the whole inside of the Caldeira, across to the villages of Luz and Pedras Brancas, Pico Timão and the Serra das Fontes.

The Caldeira is a Natural Monument, a core zone of the Graciosa Biosphere Reserve and a listed geosite, and its wetland is a Ramsar site. Stay on the paths, take your rubbish out, and leave the plants in the crater where they are.

A realistic plan for one day on this end of the island:

• Morning: the rim walk from Luz if the sky is clear, or the Maria Encantada tunnel if it is not.
• Midday: the Furna do Enxofre, inside the visitor centre's hours.
• Afternoon: down to Carapacho on the south coast for a swim in the sea pools or a thermal bath.

If you only have half a day, drive in, do the cave, and walk through the Maria Encantada on the way out.

How many steps are there down into the Furna do Enxofre?

There are 183 steps on a spiral staircase inside a tower 37 metres high. You climb back up the same way, so allow for the effort on the way out.

How much does the Furna do Enxofre cost?

In 2025 an adult ticket was 5 euros, juniors and seniors paid 2 euros, children up to 6 went free and a family ticket was 10 euros. Prices can change, so check before you go.

Is it safe to go into the cave?

The cave floor gives off carbon dioxide, and the site is monitored continuously for that reason. When the readings are too high, the cave is closed to visitors, as happened in July 2007. The visitor centre shows the current values on screens before you go down.

Can I walk around the Caldeira rim?

Yes. The official trail PRC05GRA is a 9.7 kilometre loop from the church in Luz, graded hard and taking about three and a half hours. It follows the ridge and passes the island's highest point at 405 metres.