A nuclear bunker has fallen from a clifftop into the sea after years of coastal erosion.
The red brick building stood at Tunstall in East Yorkshire for nearly 70 years, but is now being washed over by waves.
The Tunstall Royal Observer Corps building is understood to have been constructed in 1959, but was decommissioned in the early 1990s.
Historical engineering group Subterranea Britannica says the building was one of a number of nuclear monitoring posts across the UK.
The structures were intended to assess the impact of nuclear detonation and fallout levels, as well as offer vital information about radiation to help inform government policy.
Amateur historians Davey Robinson and Tracy Charlton have been charting the gradual collapse of the cliffs on which the building stood in a series of YouTube videos.
Mr Robinson has vowed to continue documenting the story of the bunker and its eventual fate.
He told the BBC: "The story of it just captured people's hearts. So many people have been invested in it – it's not just bricks and mortar, it's something else."
Experts from the Environment Agency say the Holderness coastline off East Yorkshire is eroding at an average rate of 6.5ft per year.
Despite fascination with the ruined bunker, East Riding of Yorkshire Council has warned the public to stay away from the eroding cliffs which may prove hazardous.
A local authority spokesman added that the former bunker stood on privately-owned land that is nevertheless part of the council's shoreline management plan.
He said: "The coast is undefended in this area, which allows coastal processes to continue. The Ministry of Defence originally requisitioned the land to build the structure. But following its closure, the land was returned to the landowner, which included any military infrastructure upon it."
