The Nursemaids' Tunnel, completed in 1821, was built to allow residents of Park Crescent access to Park Square Gardens. It ws built to the design of John Nash and avoids the need to cross the busy Marylebone Road (at the time known as New Road). Its name comes from the presumed use by nannies taking their employer’s infants through the tunnel by pram.
In 1854 the tunnel was strengthened with cast iron (versus the original Yorkshire flagstones) where it passed over the newly-built Metropolitan Railway. In World War II it was used as an air-raid shelter. It is listed at grade II. Although it remains in private hands, the tunnel is usually accessible during the annual London Open Squares weekend.