A secret collection of model trains that needed its own house in southern New South Wales and came with a staff bound by confidentiality agreements is being documented at the Workshops Rail Museum, west of Brisbane.

Key points: Giant collection once belonged to late businessman

Giant collection once belonged to late businessman Models were once stored in their own house

Models were once stored in their own house Museum says collection is worth 'millions'

Some 11,000 pieces — including locomotives that have working lights or can billow smoke — have been donated to the Ipswich museum.

That represents about half the collection from the estate of late Wollongong businessman Marsden Williams.

Workshops curator Dr Geraldine Mate said the museum usually focussed on Queensland rail history, but that this was a collection they could not pass up.

"We know of very few collections, if any, that are like this that exist in the world," she said.

"[Mr Williams's] employees found it very hard to speak on camera because they'd spent, you know, 30 or 40 years not speaking about the collection."

Mr Williams had a building constructed to house his collection, calling it the T House, and had a full-time technician to care for it.

A Bockholt model of a JA Maffei Munchen 96 class freight locomotive. ( ABC News: Alyssa Betts )

The T House had two levels — one full of display cases for his favourite pieces handcrafted after trains from 11 nations.

The second level was for his custom-designed model railway layouts that had 4.5km of nickel-silver track, and were capable of running 20 trains at once.

"I walked in the door (to the T House) and the hair rose on the back of my neck and I was just blown away," Dr Mate said.

Valuable models contain staggering detail

Workshops collection manager Rob Shiels has the job of cleaning, measuring, photographing and recording each of the items.

He estimated the entire project would take him 40 years, at the pace he was going — alongside his other responsibilities.

"The sheer volume was just astounding. I thought … we best just crack in and start getting through it," Mr Shiels said.

He said some of the models were extremely rare, and were "by no means toys".

A New South Wales AD60 Beyer-Garratt steam locomotive train. ( ABC News: Alyssa Betts )

"The engineering design and fabrication of these models and the amount of work that would've gone into them would be staggering," he said.

"Inside the cabins are painted, there's moving parts … and there's very, very high quality motors.

"Other models have light switches that'll turn the lights on these models, so when they're on the layout and drawing power you can turn switches so lights will come on.

"There's sound effects as well … and also some of them will blow smoke."

A Deutsche Bundesbahn 86 tank locomotive. ( ABC News: Alyssa Betts )

Dr Mate would not give an exact value for the collection, but said it was worth millions of dollars.

For now, items are only being displayed on the museum's website as they are progressively recorded — although physical displays are planned for down the track.

For train fanatics, the delay may just be worth it.