Terceira: Inside Algar do Carvão and the Lava Tubes

Every cave tour on Terceira visits some combination of the same three places, and the marketing tends to blur them into "the caves". They are structurally different and worth telling apart before you book.

Algar do Carvão is the chimney. A column of lava drained back down its own vent and left the pipe standing, and the pipe is what you descend. Radiocarbon work puts it at 2,148 years old give or take 115, which is more precise and more defensible than the "about 3,200 years" that circulates in guidebooks. Inside it is 12 to 13 °C all year, the walls carry silica stalactites that are unusual enough to be the reason it is a Regional Natural Monument, and a lake of rainwater sits at the bottom. Entry is 10 EUR, visits last about half an hour, and 150 people may be inside at once.

Gruta do Natal is a lava tube: a horizontal tunnel where a flow crusted over and kept running underneath. Furnas do Enxofre is neither, an open fumarole field near Porto Judeu where volcanic gas comes out of the ground at a range of temperatures, some of them high enough to be fenced.

This is the fact that every other page about Terceira puts last, and it should be first.

From October to March, Algar do Carvão opens on four days a week only: Tuesday, Wednesday, Friday and Saturday, from 14:30 to 17:00. Two and a half hours, four days. If you land on a Sunday in November for three nights, there is a real chance you never get inside the thing you came for, and no amount of paying will change it, because there is no online booking. Tickets are sold at the door, and the ticket desk does not take American Express.

Gruta do Natal is stricter still out of season. Outside the summer opening it is available only by prior arrangement, with 48 hours' notice and a charge of 300 EUR for the group. That matters because the combined cave tours sold at 45 to 50 EUR are priced on the assumption of ordinary summer opening. A December booking for a combined trip is buying something that does not exist in that form at that price, and the substitution is a different lava tube rather than a refund.

In summer the problem disappears. From April the site runs daily hours and the caves are the easiest thing on the island to arrange.

This is uncomfortable and it is better said than hidden. Of the four Terceira products on this site, two carry a notice in their own text saying Algar do Carvão is not accessible and that a substitute lava tube will be shown instead. One of the two dates its notice to 19 October 2024 and describes the reopening date as unknown. The other says the site is temporarily closed for maintenance and adjusts its itinerary accordingly.

The other two sell Algar do Carvão without any caveat at all.

Both cannot be current. A closure notice left in a listing for two years is a listing nobody has read since, and the far more likely reading is that the site reopened and the text was never updated. But that is a deduction, not a booking condition, and the amount you are risking is the entire reason you chose this island. Message the operator before you book and ask one question: is Algar do Carvão open on the day of my tour. A straight answer takes them thirty seconds and it is the single most useful thing you can do about Terceira.

Terceira is four overlapping stratovolcanoes on the Terceira Rift, and they are in age order across the island. Cinco Picos is the oldest at roughly 370,000 years and is now worn down to low ground. Guilherme Moniz follows at around 270,000, and its crater rim at 640 metres is where the road to the caves runs. Pico Alto is much younger, active between about 9,000 and 1,000 years ago, and Algar do Carvão belongs to its system. Santa Bárbara is the youngest and the highest, 1,023 metres, and it is the only one that has erupted since people arrived.

That eruption was in 1761, on Santa Bárbara's eastern flank, and it is the only one on land in the island's written history. The most recent activity anywhere near Terceira was underwater: a submarine eruption off Serreta, at the western tip, which ran from 1998 into 2001 and produced floating lava balloons that fishermen scooped out of the sea. Nothing about it was visible from a viewpoint.

Angra was founded in 1534 and is the oldest city in the Azores. It was a compulsory stop for the fleets coming back from the Indies and the Americas, which is why a town of its size has that many churches, that much fortification and a volcanic cone with a fortress on it. Monte Brasil, the cone above the harbour, is a tuff ring built by an eruption in the sea, and the walk to the top is free and takes about an hour.

On 1 January 1980 an earthquake of magnitude 6.9 struck fifty kilometres west of the town. It killed more than sixty people, injured over four hundred, left around twenty thousand homeless, and destroyed roughly seventy per cent of the houses on Terceira, the historic centre included.

UNESCO inscribed Angra do Heroísmo on the World Heritage list in 1983, three years later, while the reconstruction was still going on. So the sixteenth-century town you walk through is genuinely sixteenth-century in plan, in facade line and in a great deal of its stone, and it was also put back together within living memory by people who had just lost their houses. Nobody selling you a tour will mention this and it is the most interesting thing about the place.

The fourth product on this page is not a cave at all. It is a five-hour wine tour at 110 EUR that runs to Biscoitos on the north coast, where vines grow in black lava inside the same kind of walled enclosures used on Pico, and finishes with a tasting in the garden of an Azorean family at Praia da Vitória. Three wines minimum, full bottles on the table, plus fortified wines and homemade liqueurs, and a rating of 5.0 from everyone who has left one.

The listing opens with a claim worth handling at arm's length: that only eight places in the world produce volcanic wines. That is a marketing figure rather than a viticultural one, and there are considerably more than eight. The supporting statement in the same paragraph is the sound one, and it is the interesting part anyway: volcanic soils cover roughly one per cent of the world's land surface and account for a much larger share of the wine anybody argues about.

Note the museum's closing days. The Biscoitos wine museum shuts on Sundays and Mondays, and the operator substitutes another producer when it does.

Four Terceira specifics, three of which cost money and one of which costs you the trip.

Cave entrances are not in the tour price. One operator states 8 to 15 EUR per person for the caves; another excludes the Gruta do Natal ticket by name. On a 45 EUR half day that is a quarter again.

There is no online booking for Algar do Carvão. Tickets are sold on site, and American Express is not accepted. Carry another card, or cash.

338 steps is 338 steps in both directions. Two of the listings mark the tour as not recommended for travellers with poor cardiovascular health and ask for a moderate level of fitness, which is a fair description. There is no lift and there is no alternative route out.

Check the timetable before you book the flights, not before you book the tour. Winter opening is four days a week for two and a half hours. If Algar do Carvão is the reason you chose Terceira over another island, that calendar should be choosing your dates.