Faith and fortitude, presumably. Seems to be the back door to the yard behind the modern office building St Catherine's Court, apparently Clifton's only Grade "A" office building, according to their blurb.
According to Bristol and Region Archaeological Services, the builder of the Pro Cathedral up the hill first tried to build the Pro Cathedral, ran into quite a lot of difficulties caused by land slippage, and went bankrupt. In the meantime, however, he managed to put up a small chapel to St Augustine of Canterbury. Then (in 1848) a convent and schoolhouse were added, and a group of Dominican nuns devoted to St Catherine of Sienna moved in, hence Catherine's Court.
St Catherine is patron saint of Europe, among other things.
GPS Coordinates:
51.45636, -2.60886
Location: Queens Road