The Tynemouth Watchtower, on Percy Gardens, was built during the First World War as a command tower for the Tyne Turrets, which were located to the north at Hartley and the south at Marsden, South Shields.
It was used as a lookout post during the Second World War before it was sold by the Ministry of Defence in 1967.
The structure, which property agents Hive Estates said is the second oldest reinforced steel building in the country, has been a three-bedroom home ever since.
The top floor of the property, formerly the roof and home to a gun installation, has been converted into an observatory and a terrace with beautiful views of Tynemouth Castle, Longsands, and the Cheviots.
The floor below, the original look out, is now a living room with panoramic windows.
The uniquely-shaped building, a mix of Art Deco and brutalist styles, also features three bedrooms, a fitted kitchen, a mid-century style bathroom, and a private yard.
The current owner of the home has held it since 2000.
