The Royal Mile is a succession of streets forming the main thoroughfare of the Old Town of the city of Edinburgh in Scotland. The term was first used descriptively in W M Gilbert’s Edinburgh in the Nineteenth Century , "...with its Castle and Palace and the royal mile between", and was further popularised as the title of a guidebook, published in 1920.From the Castle gates to the Palace gates the street is almost exactly a mile long and runs downhill between two significant locations in the royal history of Scotland, namely Edinburgh Castle and Holyrood Palace, hence its name. The streets which make up the Royal Mile are Castlehill, the Lawnmarket, the High Street, the Canongate and Abbey Strand. The Royal Mile is the busiest tourist street in the Old Town, rivalled only by Princes Street in the New Town.

More details: https://en.wikipedia.org/wiki/Royal_Mile