Liz Edwards, the wife of the Fantasy Cave's president, Ces, said the cave dweller's relationship with TrustPower was special.
"They've been so good to us. It's not just the financial donation, they encourage us and give us advice on our rather large power bill too," she said.
"This cheque will help to pay for a large, powerful and expensive battery for our stairwalker, with the balance being used for our next project.
"The contribution from TrustPower is absolutely fabulous and helps us out no end.
"The money helps us to meet our extra expenses because nothing is cheap anymore."
What does remain cheap is the entry fee to the cave where visitor numbers are improving dramatically.
"Things are looking positive and we had the best September in three years," Mrs Edwards said.
"We've also had more bookings for November than we've ever had, with a big increase in over-60s groups and friendship groups. The first bookings from school groups for December are also coming in."
During the school holidays, the cave dwellers are holding storytelling sessions at 11am and 1.15pm and the new Puss in Boots display has opened.
The Dannevirke Fantasy Cave is open during the school holidays on Tuesday, Thursday and Saturday from 10am to 2pm.