The building was rescued from imminent collapse, and appears now much as it would have done in about 1635
The largest restored medieval aisled hall in Wales celebrates its 550th anniversary this year with a series of special weekend events.
Tŷ Mawr near Castle Caereinon is also featured in an upcoming television documentary to mark the event.
The building will open its doors to visitors on the first weekend of every month from June to September.
These events will consist of a costumed guided tour and medieval living history displays in the grounds.
The initiative is supported by the local heritage group, History Matters, and re-enactors from the Montgomery Levy living history society.
Tŷ Mawr will also feature in a documentary as part of S4C's Houses of the Welsh Countryside series, produced to celebrate the reprinting of the landmark publication.
The medieval hall house features in the first episode and is described by Dr Peter Smith - formerly of the formerly of the Royal Commission on the Ancient and Historic Monuments of Wales (RCAHMW) - as his most spectacular discovery.
The documentary will be shown later this year and features interviews with the RCAHMW chairman, Dr Eurwyn Wiliam.
Tŷ Mawr is a rare surviving example of a Medieval Aisled Hall House dating from 1460.
in 2000 the house won a Building of the Year award
When rediscovered in 1971, the house was in an advanced state of disrepair and extensive restoration work was undertaken by the Powis Estate with grant aid from Cadw, the Welsh Assembly government's historic environment service.
The building was rescued from imminent collapse, and appears now much as it would have done in about 1635.
It is now a Scheduled Ancient Monument, and in 2000 the house was given the Building of the Year award by the Royal Institution of Chartered Surveyors.
Gary Ball, project officer with History Matters, said: "Tŷ Mawr is a rare surviving example of an important late medieval house typical of the Welsh Marches and one of Wales' lesser known architectural gems.
"Our aim is to encourage and promote a greater understanding of medieval history and these open weekends offer a unique insight into the life of medieval Wales."
Tŷ Mawr is open between 1100 BST and 1600 BST on 5 and 6 June, 3 and 4 July, 7 and 8 August and 4 and 5 September 2010.