Work has started on a £1.3m project to repair and restore the derelict east and south wings of the mansion house at Aberglasney Gardens.
The gardens at Aberglasney date back to the 15th Century.
It will also see the creation of a new glass roof garden and the completion of the courtyard garden, expected to open to the public next summer.
It is the latest phase of work at the Carmarthenshire gardens which date back to the 15th Century.
Restoration began in the late 1990s and it is now one of the most popular tourist attractions in Wales.
Previous work on the mansion, carried out in 1999, included external restoration work of the north and west wings and the reconstruction of the Portico entrance.
Now the derelict east and south wings will be brought up to the same standard with the rooms to the rear of the mansion being covered with a glass atrium.
This will create a winter garden with the aim of making the 10-acre site an all-year attraction.
The east and south wings will be repaired as part of the project
Graham Rankin, director of operations at Aberglasney, said: "This next phase of work is very exciting and we believe the new courtyard is a one off, with no other garden like it anywhere in the world.
"There has been so much interest to date from the public and the media and the latest work is expected to further raise our profile as one of the most exciting restoration projects in the UK.
"We are looking forward to welcoming even more visitors through the gates next year to see the latest features."
Funding has come via the Wales European Funding Office of the Welsh Assembly and Cadw, as well as a private charitable foundation.
The trustees at Aberglasney have further plans to restore the interior of the mansion and are raising money through appeals.