The northern approach to Edinburgh Castle consists of a narrow spine of land that slopes down to the south and especially to the north. There were buildings on the north slope separated by narrow lanes. One can think of those lanes as ribs ascending to the spine/backbone of the Royal Mile, the road that leads from Holyrood Palace up to the Castle. Premium real estate was along the Royal Mile, and so there was an economic interest in extending building platforms to the north and south. As these extended, many lanes were capped off by building projects that gobbled up the "air real estate" while leaving those on the ground covered up by the newer buildings. The residents and business owners below weren't the richest of people, so that did whatever they could to continue existence, managing their businesses and their lives, now largely in the darkened basements of other people's buildings. Mary King's Close is not underground; it is under building.

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