The city one storey above itself: underground Prague

Prague did something few cities have done: it lifted itself. The Old Town you walk today stands several metres above the Old Town of the twelfth century, and the difference did not erode away — it is still down there, room by room.

Why the streets were raised

The Old Town sits on the inside of a bend in the Vltava, on ground barely above the water. Medieval floods were regular and ruinous, and in the thirteenth century the town responded with an enormous, generations-long piece of civil engineering: the ground level of the whole district was raised — by two to three metres in most places, more near the river — with earth and rubble.

The consequence is the defining fact of underground Prague. The Romanesque ground floors of the town's stone houses became cellars. Doorways that once opened onto streets now open onto packed earth. Several dozen Romanesque houses survive below modern ground level in this way — a twelfth-century town preserved not as ruins but as basements, sitting under the Gothic and baroque city that grew on top.

You can stand in that buried town. The Old Town Hall — the building of the Astronomical Clock — runs tours of its underground, where Romanesque and Gothic halls that were once at street level now form a chain of vaulted rooms below the square, complete with a medieval dungeon. The House of the Lords of Kunštát on Řetězová street keeps one of the finest Romanesque cellar halls in the city, and several restaurants and pubs around the Old Town seat guests in twelfth- and thirteenth-century spaces without making any particular fuss about it.

Vyšehrad: the fortress underground

The second underground is military. Vyšehrad, the rock fortress south of the centre, was rebuilt in the seventeenth century as a baroque fortification, and inside its ramparts run the casemates — around a kilometre of brick corridors built to move troops and supplies under cover.

The corridors lead to Gorlice, a vast vaulted hall originally meant for stores and later used as, among other things, an air-raid shelter and a vegetable depot. Since 1992 it has held something better: six of the original baroque statues from Charles Bridge, moved underground to save them from the weather. The figures on the bridge itself are copies; down here, in the half-dark, you stand next to the blackened originals. Entry is by guided tour from the Špička gate information point, and it is one of the least crowded remarkable places in Prague.

The Cold War layer

The twentieth century added a third underground, sized for a different catastrophe.

Under the hill of Folimanka in Nusle — directly beneath the pillars of the Nusle Bridge — sits Bunkr Folimanka, a nuclear shelter built for around 1,300 people, kept with its original filtration plant, decontamination rooms and diesel generators. The city opens it to the public roughly one Saturday a month, free; the schedule is worth checking, because it is the most complete Cold War interior a visitor can see in Prague. A similar shelter sits inside Parukářka hill in Žižkov, now partly a music venue.

The biggest shelter of all, though, is the one you ride every day. The metro, opened in 1974, was built to double as a fallout shelter: the deep stations — Náměstí Míru is 53 metres down — carry massive blast doors, visible as thick steel frames at some platform entrances, and pressurised sections designed to hold tens of thousands of people. The transport history tells that story properly.

The cellars that work for a living

Beer is the underground's oldest steady tenant. Lagering — the cold months-long maturation that defines Czech beer — needs constant low temperatures, and before refrigeration that meant cellars. The brewing houses of the Old and New Town matured their beer under their own floors; U Fleků, brewing since 1499, still occupies its historic cellarage, and the beer halls of the centre are very often the upper storey of something much older.

Visiting, practically

• Old Town Hall underground — tours run daily from the tourist office inside; combine with the clock tower.
• Vyšehrad casemates and Gorlice — guided entry, roughly hourly in season, from the fortress information centre.
• Bunkr Folimanka — free open days about monthly; check the city's schedule before going.
• Take a layer. Everything below ground holds cellar temperature all year — welcome in a Prague summer, a shock in shirtsleeves.
• Several commercial *dungeon* and *underground legends* tours operate around the Old Town; they use real spaces but the history is costume. The three sites above are the serious versions.

The deepest lesson of the underground is the one it teaches about the surface: Prague survived so intact partly because it kept building on top of itself rather than clearing away. The city you photograph is the lid of the one below.