A tropical glasshouse is opening to visitors for the first time at the National Botanic Garden of Wales in Carmarthenshire.
The building is the garden's largest new attraction since it opened in 2000 and it is already home to thousands of palms, orchids and giant leaves.
Guest of honour is the New York-based architect, Welsh-born John Belle.
His projects include make-overs for the Rockefeller Centre and Grand Central Terminal in New York.
Garden director Kevin Lamb said the official opening marked a new chapter in the garden's history.
Four years ago the £43m tourist attraction, which had been opened by Prince Charles in 2000, was within hours of having to call in the administrators.
But at the last minute, a rescue package was put together and the garden has slowly seen its fortunes blossom.
Mr Lamb said: "Not only is this a fabulous and important moment in the garden's short history - it is also a proud moment for Wales.
WELSHMAN CHANGING NEW YORK
Born in 1932 in Pontcanna, Cardiff, John Belle moved to New York in 1959 to launch his career in architecture
Three of his projects - Ellis Island, Grand Central Terminal and the Delaware Aqueduct - received the Presidential Design Award, the USA's highest prize for public architecture
Other projects include refurbishments to the Chrysler Building and Rockefeller Centre in New York
In 2003 he was made an honorary fellow of the Royal Society of Architects in Wales
"This further enhances the garden's worldwide reputation as a millennium project of global significance."
The glasshouse was Mr Belle's first project in Wales and he provided his services free.
He said: "Designing the tropical house - a building that is all about the connection between the world of plants and the realm of architecture - provided a wonderful opportunity for me to reconnect with my roots.
"I don't think there could have been a more appropriate project for me at this stage in my career."
Horticulturists from the garden have visited colleagues and collectors across the UK to source plants for the glasshouse.
Laura Davies said: "We have visited colleagues at Kew, Edinburgh and Glasgow botanic gardens and never came away empty handed.
"We will be growing an amazing range of plants from throughout the tropics - majestic palms, beautiful orchids, giant leaves and unusual flowers.
"I hope visitors will be as excited as we are."