If you like to go to sleep before 2-3 in the morning (and are not hard of hearing), this is NOT the flat for you! Other reviews mentioned the noise, but my husband and I live in NYC half-time, and we're used to street noise so figured it wouldn't be a big deal. I've also stayed on Grassmarket before and thought I knew what we were in for. WRONG. The bedroom looks out onto the square, and this is *next-level* noise: full-on shouting, hooting, singing, etc. starting around 11pm and ending only when the late bar disgorges its final occupants - who often spent another hour wandering around yelling at each other before wandering off. I know the apartment managers can't control the noise of the square, but they could - and SHOULD - put in some noise-mitigation measures: double-glazed windows and/or thick sound-canceling curtains would have been extremely welcome.
It's quite frustrating: the flat itself is lovely and the location is fantastic! But after three nights of essentially no sleep (delivery trucks for the restaurants and bars starting unloading and beeping around 6am, again sounding as if they're in the room with you), we couldn't wait to leave. Gutting.