The Grade II listed Durham Miners' Association hall in Red Hill, Durham City, opened in 1915 when the county's coalfield employed 200,000 men.
The red-brick mansion contains hundreds of photographs and banners, as well as a debating chamber with 300 seats nicknamed the pitmen's parliament.
The association is planning to apply to the Heritage Lottery Fund for £2m.
Among the hall's treasures is a letter written in 1943 from the USSR ambassador on behalf of Soviet Union leader Joseph Stalin. The letter thanks Durham miners for a charitable donation of £1,500 for an X-ray machine.
Chairman of the association, Alan Cummings, said: "It's about a rich, exciting heritage - hard times and good times - and that should be celebrated.  This building represents the finest of that."
But Mr Cummings said it was a struggle to pay growing maintenance and running costs.
Mining historian Dr Stuart Howard, of Sunderland University, said the miners' hall was "probably the finest trade union building in Europe".
"It was meant as a status symbol, so when negotiations went on here the status and strength of the union was communicated," he added.
Plans to turn a historic miners' headquarters into a heritage and exhibition centre have been unveiled.