WA's Supreme Court has convicted some of the State's most infamous criminals over the past century, but did you know an Aboriginal woman apparently haunts the building?

Or that a unicorn in chains looks down from above the seat where the judge presides?

On Sunday the courthouse, built in 1903, will open its doors to the public in an effort to engage with the wider community and educate people about the judicial system.

The building's criminal court has convicted thousands of people over more than a century, including notorious Perth couple Catherine and David Birnie, who killed four women in the 1980s, and businessman Alan Bond.

But what secrets has the old building kept hidden over the many years?

A kangaroo court?

The Supreme Court has kept the crest, a throwback to years gone by. ( ABC News: Briana Shepherd )

Sitting above the building, and above each judge in the building's three courts, is the full British coat of arms.

The crest depicts a crowned lion on one side, representing England, while a unicorn in chains, representing Scotland, is on the other.

According to legend, a free unicorn was considered a very dangerous beast, which is why the mythical creature is chained.

Chief Justice Wayne Martin, who has presided over the Supreme Court for the past 11 years, said the crest - which has the French phrase "Dieu et mon droit" (God and my right) - was maintained in the building because of its heritage value.

"At the time this building was built it was thought that the authority for all the judges came from the monarch," he said.

"Whereas today we accept the authority comes from the state of Western Australia, and so in our modern court buildings we sit under our state crest, which has the kangaroos on it.

"Which is good, because when anybody complains that it's a kangaroo court we can say, 'of course it is, look at the crest behind us'."

Walking in criminal footsteps

WA Chief Justice Wayne Martin says the 114-year-old Supreme Court building harbours many secrets. ( ABC News: Briana Shepherd )

Chief Justice Martin said the open day provided an opportunity to get an insight into the court's operation, with access made available to otherwise restricted areas.

Visitors will also be given the chance to follow in the footsteps of some of WA's worst criminals, and walk the stairs from the holding cells up to the dock.

"The last man who was executed in Western Australia, Mr Eric Cooke, was convicted here and sentenced here and ultimately executed, and many of the other more notorious criminals of the earlier part of the last century were also dealt with here," Chief Justice Martin said.

"I'm sure it would have been a very frightening experience for many of the people who've had to walk down those stairs after being sentenced to a long term of imprisonment, or perhaps to death."

Ghost stories

The building's darker side has been an ongoing source of fascination for visitors, the Chief Justice said.

"There have been a lot of stories about ghosts in the basement," he said.

"We have security 24/7 so people who work here still maintain those stories, they hear clunks in the middle of the night," he said.

"There's supposed to be the ghost of an old Aboriginal lady living in the cellar.

"We did have some ghost hunters in, [but] they weren't able to find anything, unfortunately."

Prisoners on the loose

WA's Supreme Court building is 114 years old. ( ABC News: Briana Shepherd )

In 2004 nine prisoners overpowered security guards and made a dash for freedom from the heritage building.

The men — all classified maximum or medium security prisoners with offences ranging from armed robbery and aggravated burglary to assaulting a police officer — were in the holding cells when the breakout took place on the morning of June 10.

"As a consequence of that escape … a significant amount of money was spent improving the custody arrangements in the cells," Chief Justice Martin said.

"We now have much more secure arrangements in our cells than we did prior to that tragic event."

Both the building and the judiciary it serves have undergone a number of upgrades and changes.

Designed by well-known colonial architect John Grainger, the court was built before electricity was readily available.

Multiple large windows for natural light are in each room, as are fireplaces in every corner.

"One of the jobs of the judge's orderly was to stoke the fire during the course of proceedings during winter, to make sure people didn't get too cold," Chief Justice Martin said.

Horse's hair ditched

Horse hair wigs for WA judges were abandoned in 2008. ( ABC News: Briana Shepherd )

Technology has meant many changes, with full digitisation expected either late this year or early next year, while the appearance of judges has also evolved.

Traditional robes, which some compared to looking like Father Christmas, have been replaced by plain black robes, and in 2008 wigs were abandoned

"The removal of the wigs was an important, symbolic step in showing that the courts are vibrant, contemporary, Australian institutions, rather than antiquated European institutions," he said.

There was also an added bonus for ditching the head attire.

"The wigs are made from hair of the tail of a horse," he said.

"And if you think about where the tail of the horse is anatomically — well, enough said."

The Supreme Court will be open to the public between 11am and 3pm on Sunday October 15.