Castillo de San Felipe

From outside there is not a great deal to look at: low walls, broken masonry, batteries set above the water at the harbour mouth. The interest is underneath. Kilometres of galleries were dug by hand beneath the fortress, and while the buildings above were blown up and levelled twice over, the tunnels came through the bombardment largely intact — an underground town of passages and stairs. Enough survives above ground to read the size of the place and the job it was built for: it was raised against the Ottoman fleet in the western Mediterranean, and under British rule it served as a naval arsenal supporting Gibraltar. The galleries are seen only with the guide, and that is where the visit earns its two hours.

• Book first. Visits are by guided tour on military ground; turning up without a booking can mean a closed gate.
• Allow two hours. The tour covers the ruins above ground and the tunnels below, all on foot.
• No toilets on site — the nearest are about 380 m away in a straight line, and there is no drinking water nearby, so bring your own.
• A car helps. The parts of the site sit apart from one another, and moving between them is easier by car.
• Published opening information has not matched what happens at the gate, so confirm your slot when you book.

The castle sits on the southern side of the mouth of Mahón harbour, past the houses of Es Castell, and driving is the straightforward way in. Parking sits within about 300 m of the site in a straight line, so almost nothing is left on foot. By bus you finish the journey walking: the nearest stop, Esglèsia des Castell, is about 1.6 km off, and Fontanelles about 2 km. The Camí de Cavalls, the coastal path that rings Menorca, passes close by, and its information board stands about 560 m from the castle. Once you are on the site, the areas of interest are separated, and a car is useful for getting between them.

Best: whichever tour slot you can get — the site opens for booked tours at set times, and there is no dropping in between them.

Avoid: arriving without a booking, which is how people end up outside a locked gate at the end of the journey out.

Most of what you came for is underground, so a grey or wet day costs little here; the tour timetable decides the visit, and the weather barely comes into it.

This is military ground, and it is not open to walk into: the castle is seen on a booked guided tour, and the underground galleries only in the guide's company. The ruins are managed together with the other fortifications of Mahón harbour by the Consorcio del Museo Militar de Menorca, which has recovered part of the gallery system since 1998. Only some of it has been opened to visitors, and the rest stays shut.