07 September 2026 • 6 min read
Furna do Enxofre sits inside the Caldeira of Graciosa Island at 300 meters above sea level. You reach it through a 200-meter tunnel bored through the crater wall, then descend 183 steps on a spiral staircase into a cave that opens into a space roughly 200 meters across, with a sulphurous subterranean lake at the bottom and a dome of basalt lava prisms overhead. A natural opening in the ceiling acts as a skylight. On clear days around noon, a beam of light reaches the water below. There is nothing else like it in the Azores.
Entry: Ticketed and guided only | Duration: Approximately 1 hour | Book ahead: Required in July and August
What Is Furna do Enxofre
Furna do Enxofre is a lava tube cave formed during the last volcanic eruption inside the Graciosa Caldeira. The eruption created a gas-rich environment that produced the cave's most distinctive features: the domed ceiling of hexagonal basalt prisms, similar in structure to the Giant's Causeway in Northern Ireland but overhead rather than underfoot, and the sulphurous lake at the cave floor, fed by geothermal activity that has continued since the eruption.
The name translates roughly as "Sulphur Cave." The smell of sulphur is present but mild at the entrance; inside the cave the air is stable and the smell dissipates. The cave temperature is consistent year-round at approximately 14 to 16°C (57 to 61°F), notably cooler than the exterior, which is relevant in summer.
The cave is protected as a natural monument under Portuguese and European law. Entry is managed by the Regional Government of the Azores, which limits group sizes and requires all visits to be guided to protect the cave environment.
The Skylight Phenomenon
The most discussed feature of Furna do Enxofre is the natural opening in the cave roof. On clear days, around solar noon (approximately 13:00 to 14:00 local time in summer), sunlight passes through the opening and reaches the water surface below. The light column is visible from the spiral staircase and from the viewing platforms inside the cave.
The effect is weather-dependent. On overcast days, the skylight lets in diffuse light but not the direct column. Visiting at midday on a clear summer day gives the best chance of seeing the full phenomenon. The tourist office in Santa Cruz can advise on forecast conditions.
The opening also serves a geological purpose: it is the primary ventilation point for the cave, which is why the internal atmosphere is stable despite the geothermal activity below.
The Spiral Staircase
The 183-step iron spiral staircase is the physical centerpiece of the visit. It was installed in 1939 during the first systematic exploration of the cave, replacing earlier rope and ladder access. The staircase descends from the tunnel entrance down through the cave walls to the viewing level near the lake.
The descent takes about 10 minutes. The staircase is well-maintained and has handrails throughout. The footing is dry. Visitors who are uncomfortable with enclosed spaces or with heights should note that the staircase is open on one side and the cave ceiling is visible above and below throughout the descent. It is not a confined tunnel.
The view from the lowest platform, looking up through the staircase to the skylight and then across the cave to the lake, is the best single vantage point in the site.
VISIT FURNA DO ENXOFRE
Furna do Enxofre is included in guided island tours of Graciosa that also cover the Caldeira, Ponta da Barca, and the south coast. The cave is the primary attraction on the island; most tours are built around the morning visit.
Browse Graciosa Tours →How to Get There
Furna do Enxofre is inside the Caldeira nature reserve on the central plateau of Graciosa Island. The access road climbs from Santa Cruz da Graciosa to the Caldeira rim, then continues inside the crater to the cave entrance. The drive from Santa Cruz takes approximately 15 minutes.
There is a small parking area at the tunnel entrance. Buses from Santa Cruz serve the Caldeira during peak season on a limited schedule; for most visitors, a rental car or a guided tour is the practical option.
The entrance to the 200-meter tunnel that leads to the staircase is marked with an interpretation panel and ticketing booth. There are toilets at the surface level.
Visiting Independently vs. Guided Tour
Entry to Furna do Enxofre requires a ticket and a guide regardless of how you arrive. The Regional Government provides guides at the cave entrance during opening hours; if you drive yourself, you join the next available guided group at the site.
The alternative is to book a guided island tour from Santa Cruz, which includes transport, the cave entry, and visits to the Caldeira, Ponta da Barca lighthouse, windmills, and other sites. This is the more practical option for visitors without a car and adds context that the on-site guides provide more briefly.
Independent drivers should check opening hours before visiting. The cave is typically open Tuesday to Sunday during the main tourist season, with Monday closures for maintenance. Hours vary by season; confirm at the Graciosa tourist office or the cave's official page before planning around a specific time.
What to Wear and Bring
The cave interior stays at 14 to 16°C (57 to 61°F) regardless of external temperature. In July and August, the temperature difference from the exterior is significant; bring a light layer even in high summer. The descent is not physically demanding, but the staircase has 183 steps to descend and then re-ascend, so appropriate footwear matters. Flat-soled shoes or sandals are not suitable; closed shoes with a grip sole are recommended.
Photography is allowed. There is enough ambient light inside the cave for photography without flash, though the conditions at the lower viewing level near the lake are dim. A phone camera performs adequately; dedicated camera equipment is permitted.
Combining with the Caldeira and Furna da Maria Encantada
The most common way to visit Furna do Enxofre is as part of a Caldeira half-day. The cave visit takes approximately 1 hour. Afterwards, the Caldeira rim trail (1.5 to 2 hours) and the descent to Furna da Maria Encantada (30 to 45 minutes additional) complete a full morning covering the three main geological sites in the center of the island.
This sequence places Furna do Enxofre first in the morning (when groups are smaller and the site is less crowded), the rim trail second (best light is morning to midday), and Furna da Maria Encantada third (afternoon light inside the cave mouth is the best for the interior). The total time is 3 to 4 hours with moderate walking.
Graciosa Island Vacation Packages
Flights, accommodation, and rental car arranged together. Furna do Enxofre is the primary attraction on Graciosa; packages ensure you have transport to the Caldeira and a flexible schedule for the cave visit.
Keep reading
Frequently Asked Questions
What is Furna do Enxofre?
Furna do Enxofre is a lava tube cave inside the volcanic Caldeira of Graciosa Island in the Azores. It contains a subterranean lake of sulphurous water, a ceiling of hexagonal basalt lava prisms, and a natural skylight that admits a column of sunlight at midday on clear days. It is reached through a 200-meter tunnel and a 183-step spiral staircase. Entry is ticketed and guided; it is the primary natural attraction on Graciosa.
How do I visit Furna do Enxofre?
Entry requires a ticket and a guided visit; independent self-guided access is not permitted. You can either drive to the Caldeira independently and join a guided group at the entrance, or book a guided island tour from Santa Cruz da Graciosa that includes transport and the cave entry. The latter is the more practical option and provides more context. Book in advance in July and August when slots fill.
How long does the visit to Furna do Enxofre take?
Approximately 1 hour for the guided cave visit, including the tunnel walk, the staircase descent and ascent, and the guided explanation at the viewing platforms. Adding the drive from Santa Cruz (15 minutes each way) and the Caldeira rim walk (1.5 to 2.5 hours) makes a half-day of 3 to 4 hours in total.
Is Furna do Enxofre suitable for children?
Yes, with some considerations. The staircase has 183 steps with handrails and is safe for older children and adults of normal fitness. The descent and re-ascent is the main physical demand. The cave is not dark; ambient light is sufficient throughout. Children who are uncomfortable with enclosed spaces or loud echoes should be prepared for the cave acoustics. There is no age restriction.
What is the best time of day to visit Furna do Enxofre?
Around midday (13:00 to 14:00 local time in summer) on a clear day, when the natural skylight sends a column of light down to the lake. Morning visits are less crowded. If seeing the light column is a priority, plan for midday; if avoiding crowds is the priority, arrive when the site opens. The site is typically busiest between 10:00 and 14:00 in peak season.
Is Furna do Enxofre open year-round?
The cave is typically open Tuesday to Sunday during the main tourist season, with Monday closures. Opening hours vary by season and are shorter outside peak months. Confirm current hours with the Graciosa tourist office or at the Regional Government of the Azores website before visiting, as schedules change annually.
