Called "The Barn" in earlier times, it is thought to be the oldest stone building surviving in the lower North Shore and is claimed to be "the last maritime industrial structure remaining in Sydney dating from the early Colonial period".

[3][1] By 1838 when Mosman owned 44 hectares (108 acres) along the local waterfront, he decided to sell his whaling interests and retire to a country property near Glen Innes.

[2][1] The Barn subsequently had a range of uses, including being the site of the first meeting that led to the formation of the Mosman Municipal Council, a roller skating rink and other uses.

The entire site was then declared dangerous, due to mud and rock slides from an unstable cliff behind the Barn and the risk of a block of home units coming down on top, resulting in the temporary relocation of the scouts.

It has walls of narrow-coursed squared sandstone rubble with more substantial quoin stones, some window dressings and lintels, and basework.

[1] The lintel over the wide main doorway appears to be concrete and there is a metal-barred toplight above the transom of the timber double doors.

[1] Beside the main doors there is a stone base bearing a plaque dedicated in 1981, on which the significance of the building is briefly set out.

[1] In front of the building are rare, mature African yellow wood/plum pine trees (Afrocarpus falcatus (syn.

[1] Associated with Archibald Mosman, after whom the suburb was named, "The Barn" is believed to be the oldest stone building surviving in the lower North Shore and Sydney's only remaining maritime industrial structure dating from the early Colonial period.