A stone and brick conduit gulley that was part of a system of conduits under Greenwich Park that supplied water to the Royal Hospital for Seamen (now the National Maritime Museum).
It is located near (just east of) the Queen I Elizabeth Oak at the centre of the park.
More info in this blog by Running Past: https://runner500.wordpress.com/tag/greenwich-hospital-standard-reservoir/
64 photos taken in November 2020 with a Sony a6000 and processed in Reality Capture.