Looking from below, this is a spiral staircase in the south west tower of St. Paul's Cathedral. It consists of 88 stone stairs, that rise in a spiral 50ft up into the Cathedral. Designed by Sir Christopher Wren in around 1705, it was built by William Kempster and the design is ingenious. Each step is barely embedded in the wall, just 150mm, so it almost appears to float, with each step mostly supported the one below. The stairs feature in the third Harry Potter film - it was the Divination staircase in Harry Potter and the Prisoner of Azkaban.

https://livinglondonhistory.com/the-hidden-rooms-of-st-pauls-cathedral/