The glasshouse contains streams, ravines and waterfalls

"It is certainly a worthwhile Millennium project because it will get better with time. It should put Wales on the map."

Local gardener Eva Ryan, 36, said: "I have been watching the growth of the garden from a distance. Now I'm here I'm totally overwhelmed. It is fantastic."

The attraction's centrepiece is the oval-shaped Great Glass House, believed to be the largest of its type in the world.

It features a tilted dome and houses plants from threatened Mediterranean environments.

Other attractions include a water discovery centre on stilts above one of seven lakes, a garden dedicated to the understanding of plant genetics and woodland containing species of trees from all over the world.

The team behind the gardens aimed to blend "history with a 21st century outlook" by incorporating buildings and parkland of an 18th century estate alongside newer developments.

Professor Charles Stirton stressed both the enjoyable and educational nature of the site.

"The infrastructure will only be as good as the opportunities it provides our visitors to learn about and enjoy nature, horticulture and landscape," he said.

Environmental awareness

With its emphasis on conservation and sustainability, commission chairman Chris Smith praised the botanic gardens' contribution to the tourism landscape.

"We are all becoming increasingly aware of our responsibility for the national environment and these magnificent gardens will play a vital role in promoting the importance of our natural surroundings and our dependence on them," he said.

The gardens, which have their official opening in July, will have another botanical attraction as a not-too-distant neighbour.

The �79m Eden Project, a millennium-funded project near St Austell in Cornwall, opened its first phase this month.

Featuring yet more vast domed greenhouses, the attraction aims to show humankind's dependence on the plant world.