The Edinburgh Vaults

The vaults are inside a bridge, and most people walking over it have no idea they are on one.

South Bridge runs through the Old Town of Edinburgh from the High Street, where it meets the North Bridge, south to Nicolson Street. It carries a continuous roadway over the steep valley that was scoured parallel to the High Street when the city's crag and tail landscape formed. Only one arch is visible, the large one crossing the Cowgate at the bottom of the valley. The other eighteen are buried: the bridge has nineteen arches in total and is almost entirely enclosed by buildings on both sides.

Below deck level are many buildings and chambers, and those chambers are the Edinburgh Vaults.

The scheme came from James Hunter Blair in 1784, in his capacity as Lord Provost, as a logical southward extension of the North Bridge that already linked the Old Town to the New. Building it meant demolishing a great deal, including the old Edinburgh Poultry Market. Robert Kay designed it and Alexander Laing built it. The South Bridge Act passed the Commons on 21 April 1785, taxes were raised in 1789 to fund the work to a plan prepared by Robert Adam, and the incomplete bridge opened to foot traffic on 19 November 1786 on planks laid across the finished arches. It was completed in 1788.

Adam's version is the one that never happened. In an episode of Unbuilt Britain for BBC Radio, the architectural writer Jonathan Glancey examined why the plan for an elegant elevated gateway into Edinburgh was rejected in favour of what was actually built.

One interior of real significance survives above your head rather than below: Goldsmiths Hall, a relatively intact room tied to the old trade guilds, invisible from outside.