Visitors to Burgh House will be stepping back in time on Sunday to celebrate 40 years since it was saved from closure.
The 1970s-style fete will be complete with stalls, games, face-painting and live music.
There will also be special displays about the campaign and the building itself.
The "ruby anniversary" celebration will take place between 11am and 5pm, and it's free to attend.
Burgh House was built in 1704 when Hampstead was a fashionable spa village. It faced peril when Camden Council found dry rot in the building in 1977. The council looked to try and sell the house to a private company, spurring locals into action. They formed the Burgh House Group, chaired by David Sullivan QC.
They launched an appeal to keep it for public use, and by 1979 the group had raised £50,000. On September 8 it was officially opened to the public.
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