Aka, the one o'clock gun, which locals ignore entirely as it's every single day but always surprises a tourist: https://www.edinburghcastle.scot/see-and-do/highlights/one-o... . There is actually a small barracks on the site as well, https://en.wikipedia.org/wiki/Redford_Barracks ; the city as a whole contains a few more barracks for various units, including a signals unit conveniently located near the main telephone exchange.