Algar do Pena

Gruta do Algar do Pena

Useful Information

Location: Parque Natural da Serra de Aires e Candeeiros in Alcanede.
Only a single lane dirt road leads to the cave entrance, it is signposted "Centro Interpretação Subterrâneo" or "CISGAP".
Open: All year Tue-Sun after appointment.
Fee: Adults EUR 4.20.
Classification: SpeleologyKarst cave
Light: LightIncandescent Electric Light System
Dimension: VR=85 m.
Main chamber: VR=40 m, Ar=1,400 m², V=125,000 m³.
Guided tours: V=3,000/a.
As far as we know this information was accurate when it was published (see years in brackets), but may have changed since then.
Please check rates and details directly with the companies in question if you need more recent info.


04-MAY-1979 protected by Decreto-Lei nº 118/79 as a Natural Park.
1985 cave discovered.
1997 opened to the public.


The Algar do Pena is a 35 m deep pothole with a huge chamber at the bottom. The cave is located in the middle of a vast number of limestone quarries. The geology of Portugal has only a few limestone areas and as limestone is important for many purposes, primarily for producing cement and concrete, it is an important economic factor. Fortunately the cave is protected by the Parque Natural da Serra de Aires e Candeeiros. The entrance to the cave is located inside a small building which contains the ticket office.

The cave is famous for its huge chamber, which is the biggest natural chamber of Portugal. It also has numerous speleothems. The chamber is not only huge but deep, the bottom is 50 m below the observation platform. As the chamber has no real floor, only almost vertical walls, there is no trail as in other show caves. It also makes little sense to give the floor size of this chamber, which is only 1,400 m². Mostly the volumes of 125,000 m³ is given, but be aware that this is only an estimate, as cave surveying does not allow to compute the volume of chambers. The cave was discovered in 1985 by Joaquim Pena who was dismantling a closed limestone quarry and named after him.

Inside the cave is the Centro Interpretação Subterrâneo (Underground Interpretation Center) located. This is the first and so far the only cave laboratory in Portugal. The cave is well developed with an elevator going down 33 m to the laboratory and an observation platform. We guess that the funding of the laboratory is responsible for this extremely comfortable access. The number of 3,000 visitors per years is definitely not enough to pay for it.