Brighton's Brighton Peace and Environment Centre has launched a survival appeal after rocketing rents forced it to quit its base.
The 20-year-old centre in Gardner Street needs £12,000 to move to a new site.
Managers said the building would close in September when its lease ran out but hoped it would reopen at a planned Environment Resource Centre if the appeal was a success.
Centre co-ordinator Rona Couper said: "All leases around here have gone up by a third. We definitely cannot afford to stay.
"It is a shame, as we had a high profile here and all sorts of people dropped in."
She said the Oxford-based Ethical Property Company was looking to open a base for organisations committed to social change in Brighton and Hove.
More than 20 groups are involved in the project but still need to identify a suitable city centre site.
The Peace and Environment Centre in the North Laine is used by thousands of people for meetings and information.
The original centre was opened by peace campaigners in Kensington Gardens in 1982.
It subsequently moved to Trafalgar Street and later to Gardner Street and expanded its work to include human rights, environmental protection and fair trade.
Managers intend to publish a booklet of the centre's 20 years.
They hope activists and volunteers will contact them with stories.
Staff will be on hand at the centre tomorrow to record tales.
The centre will raise some money by selling paper leaves and fruit for a tree where people can write their hopes for a greener and more peaceful future.
Also tomorrow, artist Nickova and musician Mr Eugene will help raise money through a song-picture show outside the centre from 2pm.
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