O'Doherty's Keep, a 14th-century tower house in Buncrana, which once belonged to the O'Doherty Clan, Lords of Inishowen from the 1300s to 1608, is to be sold by online auction next month.
The unique piece of Donegal history that was recently put up for sale has already attracted international attention.
The current owners, who are descendants of the O'Doherty Clan, have decided on health grounds that it is time to sell the Keep and pass it on to a new generation of guardians.
Auctioneer Dara Furey of Seán Furey Auctioneers said that the owners have moved on in age and want to hand it over to new custodians or guardians who, they hope, will have a kind heart and will care for the Keep in the same way that they have.
While the building is intact externally, it is roofless and the interior floors are long gone.
The owners have maintained the structure and the land around it and have had several archaeological and other expert studies carried out on it over the years.
Their vision was not just to preserve this important piece of history but to restore the Keep as a visitor attraction.
However, they feel they have now exhausted all avenues in terms of getting funding and support to make that vision a reality.
Mr Furey said the owners have tried very hard to do something with it but unfortunately were unsuccessful and it is time now to see if a new owner could realise their dream.
The Keep is a familiar landmark to the many people who use Swan Park in Buncrana and is steeped in history.
It is one of a small number of O'Doherty castles still standing in varying conditions in Inishowen and Mr Furey said it is a symbol for the diaspora who left Ulster over many hundreds of years, in particular the O'Doherty's who travel from all over to see it.
In 1608, the Keep was burned by Crown forces in retaliation for the sacking and burning of Derry by Sir Cahir O'Doherty.
In 1798, United Irishman leader Theobald Wolfe Tone was arrested in the area and was imprisoned in the Keep before his trial in Dublin for treason.
Following the death of Cahir O'Doherty the Keep was granted to Sir Arthur Chichester who leased it to Henry Vaughan, an Englishman, and his family occupied the building until 1708.
A local man, Ronald HC O'Doherty, bought it in 1969.
Sinn Féin Councillor Jack Murray feels strongly that O'Doherty's Keep is of such historical significance to Donegal that it should be bought by the county council.
"It's a hugely significant building to the whole community, dating back to the foundation of Buncrana", he said.
"This is a unique opportunity to take an historic building into public ownership and preserve its history, an opportunity that may not arise again for generations."
Mr Murray said the location of the Keep at Swan Park, which is owned by the council means the council is best positioned to buy it and he has already put it to the executive that they do this.
Swan Park, which was gifted to the people of Buncrana by Harry Swan in 1965, was devastated by floods in 2017 but has had major restoration work carried out since then and Cllr Murray believes that incorporating the castle into the park would enhance it even further.
Describing it as an opportunity not to be missed, he that the council should be ambitious in relation to the property which could attract visitors from all over Ireland and further afield.
Donegal County Council did not comment on the suggestion that it should buy the Keep.
In a brief statement, it said it was aware the Keep was for sale and added that the council "also notes the conservation status of The Keep as a National Monument under the guardianship of the state".
Dara Furey acknowledges that the status of the building means it is unlikely it could be used as a family home for instance, but he said it is restorable as a visitor attraction.
"What we are selling really is a piece of history and somebody's place in history," he said.
"There are people who would like to have something like this and become a custodian and write themselves and their family's place into history in the future".
Mr Furey said they are asking €175,000 for the Keep and "that is cheap for what is really a priceless artefact".
For a building over 700 years old, Cllr Murray said the price is an extremely good bargain and he feels the people of Buncrana would be delighted if the council bought it so that it could be enjoyed for centuries to come.
Mr Furey said they have already had an interest in the property locally, nationally and from potential buyers in the UK and US.
O'Doherty's Keep is due to be sold by online auction on 7 September.
