Brisbane's oldest building is set to be opened to the public later this month, giving visitors the opportunity to see inside the city's historic windmill.

The Spring Hill windmill sits on Wickham Terrace in the Brisbane CBD and will be unlocked as part of The View From Here exhibition at the Brisbane Museum.

Access to the popular building is extremely rare due its size and heritage listing, and this event will be the first time tours will have been taken through the structure.

Old wooden window frames in the windmill offer 360-degree views around Brisbane. ( 612 ABC Brisbane: Terri Begley )

Interested members of the public have been invited to enter a ballot for the chance to be one of only 54 people allowed to see inside on May 30.

The building has been used as a working windmill, a radio station, and was involved with one of Australia's first television transmissions.

Curator Phil Manning said the windmill has played an important role in the history of the city.

Curator Phil Manning is excited to be opening the doors to Brisbane's oldest building at the end of May. ( 612 ABC Brisbane: Terri Begley )

"The windmill is the oldest building in Brisbane – built around 1827–1828 originally as a windmill to grind flour for the penal colony and it has had a remarkable history since then," he said.

Mr Manning said people's fascination with the building comes from the lack of old structures in the city.

"Here in Brisbane we just don't have these old structures," he said.

"This old structure with an odd shape has been sitting up on a hill in the city and it has played such an important role in the city."

Narrow timber stairs wind up to the viewing deck at the top of the Spring Hill windmill. ( 612 ABC Brisbane: Terri Begley )

Opening the windmill doors

More than 800 entries have already been received by the Brisbane Museum with hundreds more expected before the ballot closes on Friday.

"The tours are limited to six people and there will only be nine 20-minute tours over the day," said Mr Manning.

"The preservation of a heritage-listed building is extremely important, and being so old the materials have had to be fixed ... the stairs are tiny, narrow and winding.

"The floors are all timber – probably built in 1861."

Inside the Spring Hill windmill looking out over the Brisbane CBD. ( 612 ABC Brisbane: Terri Begley )

Mr Manning said the windmill also offered a different view of Brisbane, looking above the trees to the high-rise buildings.

"It is one of those spaces that if the walls could talk it would be incredible to think," he said.

To enter the ballot visit the Brisbane Museum website.