Mary King’s Close is a historic close located under buildings on the Royal Mile, in the historic Old Town area of Edinburgh, Scotland. It took its name from one Mary King, a merchant burgess who resided on the Close in the 17th century. The close was partially demolished and buried due to the building of the Royal Exchange in the 18th century, and later closed to the public for many years. The area became shrouded in myths and urban legends; tales of hauntings and murders abounded.However, new research and archaeological evidence has revealed that Mary King’s Close actually consists of a number of closes which were originally narrow streets with tenement houses on either side, stretching up to eight stories high. Mary King’s Close is now operated as a visitor attraction where guests can take guided tours and learn about Edinburgh’s hidden history. The close was bricked up during the great plague of 1645 with up to 300 infected residents left to die in their homes.

More details: https://en.wikipedia.org/wiki/Mary_King%27s_Close