I compulsively enter music shops when I visit a new city, even if there’s no way I can buy an instrument. Red Dog Music, at the end of Grassmarket, is an absolute playground for musicians.
They have a good number of electric guitars and basses, and if you ask one of the super-friendly staff, they’ll put you in one of their soundproofed testing rooms, where you won’t have to worry about disturbing anyone.
Their collection of acoustic guitars is a joy to behold: walls of beautifully crafted instruments. They also have a range of pianos, synths and keyboards in the back that I like messing around with… Hey, they make weird noises. The store, bewilderingly, also houses the largest guitar in Britain, a huge all-metal resonator guitar that stands at around 3 meters! Unfortunately not for sale.
If you’re visiting from abroad, perhaps buying an instrument isn’t feasible, but Red Dog also has a range of accessories, guitar pedals, books, and magazines, and is worth visiting just to wander around for a bit.