Report on a programme of historic building recording and archaeological monitoring and recording, conducted during stabilisation and conservation works to the Curzon Earth Closet, within the grounds of Tattershall Castle. The structure is a small, simply constructed brick building, built by Lord Curzon in 1914 to provide toilet facilities to the public visitors of the newly opened castle. The works exposed the 15th century outer moat retaining wall which runs behind the earth closet, and identified that its footings are stepped out by 0.8m at its rear. No further archaeological features or deposits were recorded, due to previous disturbance and animal burrowing, although a small assemblage of redeposited medieval and post-medieval artefacts were recovered, including sherds of tablewares and numerous animal bone fragments.