Worshippers at a Carmarthenshire church are travelling 50 miles for a service in the building, which has been moved stone by stone to Cardiff.
The church has been rebuilt at the Museum of Welsh Life, St Fagans
St Teilo's Church had stood near Pontarddulais since the 13th Century.
It fell into disrepair and to save the medieval structure it was taken down and rebuilt at the Museum of Welsh Life at St Fagans.
The work has taken over 15 years and it is now welcoming members of its old congregation to mark St Teilo's Day.
Some of those who used to sit in the wooden pews when the church was at Pontarddulais are among around 65 people from the town travelling to Cardiff on Friday.
The inside has been refurbished to look like it would have done in 1520
The vicar of Pontarddulais, the Reverend John Walters, who will take the service, said: "St Teilo's was still standing when I first came here to Pontarddulais as vicar 24 years ago, but I don't think there had been a service there since about 1970.
"It was just an empty shell.
"But some of those travelling remember attending services there.
"It's something that we are very much looking forward to and people are quite excited."
He said when the idea was first raised of moving the church it did not sit well with everyone.
"We don't know what would have happened to it had it stayed where it was - it may have become just ruins," he added.
"Now I think it is a good resource for Wales and Pontarddulais is very proud that the we can show off this building to people who visit the museum from all over the world."
The church once stood on the outskirts of Pontarddulais
Although the church looks the same from the outside, the inside has been decorated to recreate how it would have looked 500 years ago.
This has been done using the traditional building methods and techniques.
Rare wall paintings, found in the church dating from the 16th Century, have also been refurbished.
It is due to officially open in October 2007 as part of the National Museum Wales' centenary celebrations.