This cell is on display at the Museum of London and is from the Wellclose Square Prison, also known as the Neptune Street Prison. It was primarily used as a debtors prison and this cell dates to around 1750, once located under the Cock and Neptune public house. Wellclose Square still exists, a short walk from the Tower of London, with the prison being used until the late eighteenth century.
And some of the graffiti etched into the walls of the cell.