It's basically in the back yard of the Trinity Rooms, which is a house on Hotwell Road that I believe once connected in some way with Holy Trinity Church. My guess would be that that is some bit of leftover architecture from some demolition or change or other and someone's taken it upon themselves to keep it there as a bit of local history. Interesting!
GPS Coordinates:
51.44984, -2.61856
Location: Hotwells & Harbourside