One end is closed by the castle and the main artery, the Royal Mile, actually made up of four distinct streets named Castlehill, the Lawnmarket, the High Street and the Canongate, leads away from it, down to the now-ruined Holyrood Abbey. Narrow closes (alleyways), often no more than a few feet wide, lead downhill on either side of the main spine in a herringbone pattern. Large squares mark the location of markets or surround major public buildings such as St Giles Cathedral and the supreme courts.
Other notable places include the Scottish Parliament Building, the Palace of Holyroodhouse, the General Assembly Hall of the Church of Scotland, the Royal Museum of Scotland, Surgeons' Hall, the University of Edinburgh, and numerous underground streets and vaults, relics of previous phases of construction. 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.
The topography for the city is known as "crag and tail" and was created during the last ice age when receding glaciers scored 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 loch, the Nor Loch, on the north. Access up the main road to the settlement was therefore restricted by means of various gates and a City Wall, of which only fragmentary sections remain (see Flodden Wall).
Due to the space restrictions imposed by the narrowness of the "tail" the Old Town became home to some of the earliest "high rise" residential buildings. Multi-story dwellings were the norm from the 1500s onwards. During the 1700s the Old Town had a population of about 80,000 residents. However, in more modern times it had declined dramatically to just 4,000 residents. There are currently approximately 20,000 residents in the various parts of the Old Town. As the population was for a long time reluctant to build outside the defensive wall, the need for housing grew and hence the buildings became higher and higher. Tragically, many of these buildings were destroyed in the Great Fire of 1824; the rebuilding of these on the original foundations led to changes in the ground level and the creation of many passages and vaults under the Old Town.
On December 7, 2002, another major fire in the Old Town engulfed part of the Cowgate. It destroyed the famous comedy club, The Gilded Balloon, and much of the Informatics Department of the University of Edinburgh, including the comprehensive AI (Artificial Intelligence) library.