Formerly a derelict chapel, married couple Martin and Sue Stephenson bought the property for £27,000, and were living in Shrewsbury when they converted it into holiday lets.
They moved into the old vestry at the property in Abergynolwyn two years ago to enjoy the beautiful scenery.
But they now want to help the Alzheimer’s Society at a time when the charity is struggling to raise funds during the coronavirus pandemic.
Martin’s father Ron, has also been diagnosed with dementia and the couple hope to move to Yorkshire to be nearer to him.
The property comprises two luxury homes, with a total of seven en-suite bedrooms, fully furnished and with a sauna, hot tub and baby grand piano.
They have to sell 330,000 tickets, which will cover the value of the building, the promotion costs and a £100,000 donation to Alzheimer’s Society.