<P> Notable buildings in the Old Town include St. Giles' Cathedral, the General Assembly Hall of the Church of Scotland, the National Museum of Scotland, the Old College of the University of Edinburgh and the Scottish Parliament Building . The area has a number of underground vaults and hidden passages that are relics of previous phases of construction . </P> <P> No part of the street is officially called The Royal Mile in terms of legal addresses . The actual street names (running west to east) are Castlehill, Lawnmarket, High Street, Canongate and Abbey Strand . </P> <P> The street layout, typical of the old quarters of many northern European cities, is made especially picturesque in Edinburgh, where the castle perches on top of a rocky crag, the remnants of an extinct volcano, and the main street runs down the crest of a ridge from it . This "crag and tail" landform was created during the last ice age when receding glaciers scoured across the land pushing soft soil aside but being split by harder crags of volcanic rock . The hilltop crag was the earliest part of the city to develop, becoming fortified and eventually developing into the current Edinburgh Castle . The rest of the city grew slowly down the tail of land from the Castle Rock . This was an easily defended spot with marshland on the south and a man - made loch, the Nor Loch, on the north . Access up the main road to the settlement was therefore restricted by means of various gates and the city walls, of which only fragmentary sections remain . </P> <P> The original strong linear spine of the Royal Mile only had narrow closes and wynds leading off its sides . These began to be supplemented from the late 18th century with wide new north--south routes, beginning with the North Bridge / South Bridge route, and then George IV Bridge . These rectilinear forms were complemented from the mid-19th century with more serpentine forms, starting with Cockburn Street, laid out by Peddie and Kinnear in 1856, which specifically improved access between the Royal Mile and the newly rebuilt Waverley Station . </P>

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