The Dunedin Gasworks is one of the only known preserved gasworks in the world. It was the first and last gasworks in New Zealand and its machines are still in good-working order.
Mr Cweorth said it was a "lovely afternoon".
"It’s an amazing milestone. It’s hard to believe it’s lasted this long and it’s still going strong."
The trust had plans to expand the museum and hoped to develop a regular market day at the gasworks soon.