Plans have been unveiled to build a third biome and an underground museum at Cornwall's landmark Eden Project.
It has brought £700m into the local economy in five years
Bosses at the attraction near St Austell hope to build the structure over the next 18 months to two years at an estimated cost of £63m.
A bid has been submitted to the National Lottery for about £50m.
It will join two existing domes to promote education and research into flora, fauna and other aspects of the natural environment.
It is hoped it will also help the Eden Project to generate new visitors, which have levelled out at about 1.2 million per year, according to latest figures.
Should the plans come to fruition, the museum will be called the Museum of Vanity. It will have a series of underground chambers, each with a guest curator.
The Eden Project is one of Britain's top tourist attractions and has pumped £700m into the Cornish economy in its first five years.