The remains of a Roman bath house, considered to be among the best preserved in the UK, are on the market for £300,000.
The baths, in private woods at Beauport Park, East Sussex were discovered in 1970 by an amateur archaeologist but have never been on public display.
Owner Colin Henshaw said any buyer would need to be interested in history.
English Heritage said it looked forward to working closely with any new owner to safeguard the important site.
The baths were excavated by Gerald Bodribb, the headmaster of a private school in nearby Hastings.
They are thought to date back to the 1st Century AD and built for officers of the Roman Navy who were overseeing an iron-working estate in the Weald.
The cold, warm and hot rooms, plunge baths and changing rooms are particularly well preserved because it was buried in a landslide.
There are also the remains of the furnaces, under-floor heating chambers, flues in the walls which provided and channelled heat around the building, and painted plaster which decorated the walls.
The structure could be reburied to preserve it for the future
Many artefacts found on the site are on display at Battle museum.
Grant applications and attempts to raise funds for a permanent building to cover the remains and open them to the public have so far been unsuccessful.
"The option of reburying the site for the benefit of future generations has been proposed by English Heritage as a sensible way forward," said Mr Henshaw.
"I believe there are other ways that are more difficult but still viable. Whoever buys it would need sufficient funds."
The sale also includes five acres of woodland and a stream.
English Heritage said the bath house, a protected Ancient Monument, was a great archaeological treasure which should be handed on to future generations for the information it holds.
"The most appropriate future for the bath house would be preservation as a monument and a resource for future archaeological investigation," it said.