The Royal Mile runs from the esplanade of Edinburgh Castle, way down the hill to Holyrood Palace and the Scottish Parliament - all the way from the peak of Edinburgh's most central extinct volcano, which looms impressively over the city's main shopping street, to the foot of the next volcano along - the elephantine Arthur's Seat.
Roughly the top third of the street is cobbled, and packed with the most egregious tartan tat imaginable - tourist kilts, souvenir whiskies, and a shop dedicated to the Loch Ness Monster... that most Scottish of beasties, whose home after all is less than a hundred and seventy miles away to the north. At Festival time, most of this section is pedestrianised and filled to heaving with performers, flyerers and above all tourists. It's quite fun for a while, if you have a high tolerance for gawping crowds, but for the most part the city's residents either steer well clear or get very good at avoiding contact with anyone while declining promotional material as efficiently as possible.
Like many Edinburgh roads the Royal Mile changes name every couple of hundred yards, presumably to befuddle any invaders or other visiting foreigners. From top to bottom it goes from being the Castle Esplanade to Castle Hill, Lawnmarket, High Street and then Canongate. It is at least blessed with a single overarching name though, which even appears on some road signs - this is in contrast to most many-titled Edinburgh streets, like the bafflingly seven-named road which is called North Bridge (or possibly South Bridge) when it intersects with the Royal Mile.
Most of the touristry is confined to Lawnmarket and the High Street - as you head down towards Canongate it slowly gives way to some quite interesting shops, little museums, and institutions like the Scottish Book Trust and the Storytelling Centre. All the way down, you get closes coming off on either side, often with their own fascinating histories and places to visit, where you can head downhill even more steeply on foot.
Like so much of Edinburgh there is an astonishing amount of really gorgeous architecture to be seen here, as well as some rather fine statues. The Castle, The Hub, St Giles' Cathedral and the old John Knox house are particularly worth seeing, but there's plenty more that you'll miss if you don't stop and raise your eyes well above the shop fronts from time to time. Right at the bottom is the very pretty, fairytale-ish Palace, and next to it the controversial parliament building, which tends to divide people firmly into 'Love' and 'Hate Hate Hate' camps. For my part I actually like quite a lot of it, from up close, but the overall impression it gives is nevertheless a formless hodgepodge of concrete and barred windows. It's fascinating, in a sense, that they managed to spend £414 million of public money on something that ended up looking like that, but aside from that it I consider it one of the less interesting buildings on a street with so much history and beauty.