Gruta das Torres

The Gruta das Torres is a lava tube formed around 1,500 years ago when the outer surface of a lava flow from Pico cooled and hardened while the molten rock inside drained away, leaving a tunnel. It runs for over five kilometres, the longest known in Portugal, and a section of it is open to guided visits from a visitor centre built of dry-stone basalt above the entrance. Inside are the features that make lava tubes worth seeing: lava stalactites where molten rock dripped from the roof, benches marking the levels the flow stood at, ropy pahoehoe surfaces, side galleries and areas of collapse. There is no artificial lighting - visitors carry lamps and wear helmets, which is deliberate and which makes the visit far better than a floodlit cave. Temperatures inside are cool and constant, and the floor is uneven basalt.

What you actually see

• The tube - over five kilometres of lava tunnel, the longest in Portugal.
• The formations - lava stalactites, flow benches and ropy pahoehoe surfaces.
• The lamps - no fixed lighting; visitors carry their own with helmets.
• The visitor centre - a dry-stone basalt building over the entrance.

When to go

Year-round; the temperature inside does not change. One to two hours. Tours run at set times and should be booked, particularly in summer.

Honest expectations

Guided tours only, at fixed times, and they fill. The floor is rough uneven basalt and there are low sections - not suitable for anyone with mobility difficulties. Cool inside; bring a layer. Closed on some days.

Nearby

The Criação Velha vineyards are alongside; Madalena and the Pico ferry are north.