A HOLY well near Helston is undergoing major restoration to rescue the stone structure from collapsing.
Volunteers joined archaeologists and builders to clear and restore Trelill Well.
The building became the first structure in Cornwall to be designated a scheduled monument in the 1920s.
It is regarded as a perfect example of a medieval well-house.
Built of local killas stone, and dating back to the 17th century, with a granite-arched doorway, the well-house has not undergone repairs or alteration for more than a century.
Archaeologist James Gossip, of Cornwall Council's historic environment projects department, said: "In the past ten years the building had started to suffer as a result of a build-up of silt against its back wall, and had become overgrown with ivy and other tree growth, with large roots loosening stones and threatening to collapse parts of the structure. The adjacent stream had also been blocked, causing water to pour through the rear wall and washing out the earth bedding mortar, leaving the structure in fragile condition."
He said restoration was vital to stabilise the structure.
A detailed archaeological survey was carried out to determine the extent of the problems and the best course of action.
Volunteers from Meneage Archaeology Group have been helping Cornwall Council's archaeologists clearing silt behind the well-house, removing vegetation and scraping loose earth from between the stones.
Mr Gossip added: "Loose stones have now been put back in place and the building re-pointed with lime mortar by building conservation specialists Joe Morris and Tim Lake that ensures the original appearance of the building is retained as far as possible."
The roof will be covered with turf by the volunteers.
Once the restoration work is completed, the area surrounding the well will be fenced off to help highlight the significance of the monument as a historic feature and secure the area around it. It is hoped a public open day will mark the completion.
The work is being funded by landowner Mark Rowe and organised by Cornwall Council's Scheduled Monument Management Project, to which English Heritage and the Cornwall Heritage Trust contribute. Wendron Parish Council has also given its support.