Cornwall's Eden Project has raised £1.5m in a crowdfunding appeal to build an education centre.
The eco-attraction in St Austell wants to turn two farmhouses into classrooms for horticulture and food production. The total cost of the project is £3m.
The charity sold £500 bonds in 20 hours in return for 6% interest a year.
Eden executive director David Harland said: "To reach our maximum of £1.5m in less than 24 hours was beyond our expectation."
The centre hopes to surround the two farmhouses and their outbuildings on the edge of its site with a new market garden.
"We thank everyone who has invested and now look forward to bringing these exciting plans to reality," said Mr Harland.
"When complete, the learning village will give young people the chance to study and work in very special surroundings within the Eden Project."
Mr Harland said the remaining £1.5m would either be paid for by Eden or possibly match-funded with grants from Europe or from other bodies.
Luke Lang, co-founder of Crowdcube which led the fundraising, said: "The blistering speed Eden Project raised its £1.5m target makes it the fastest mini-bond raise to date and is a huge vote of confidence from investors and Eden's community."
Since 2000, Cornwall has received millions of pounds of European funding to help the county's economy grow.
Mr Harland said the organisation had chosen crowdfunding because it was "moving with the times and it allows our supporters to invest in Eden".