More than 100 Queenslanders have left their mark on the Cross River Rail tunnel during a "once-in-a-lifetime tour" before rail tracks for a multi-billion dollar project are laid.
The northern portal entrance, next to the inner city bypass, was open for people to walk through on Sunday.
Members of the group signed their names on a commemorative board that will be preserved on a wall in the tunnel.
Stretching from Dutton Park to Bowen Hills, Cross River Rail is a new 10.2-kilometre rail line that includes 5.9km of twin tunnels under the Brisbane River and CBD.
Construction of the $5.4 billion project is scheduled to be completed in 2024, and following testing and safety checks is expected to be operational in 2025.
The public walked about 470 metres into the Merle tunnel at the northern portal, next to the inner-city bypass which descended about 30 metres underground.
The northern portal is where trains will enter and exit the Cross River Rail tunnels.
The group toured the Merle tunnel, named in honour of Merle Thornton AM, who famously chained herself to the Regatta Hotel bar in 1965 to protest against a ban on women drinking in public bars in Queensland.
The twin tunnel is named after the first female electrical engineering graduate in Queensland, Else Shepherd AM.
Following tradition, the boring machines were named after women and the tunnels will bear their names.
Ms Thornton's son Harold Thornton walked through the tunnel to celebrate it being named after his mother.
"It's an amazing honour for the family to have the boring machine [named] after Mum … this is going to be a fantastic thing for Brisbane," he said.
"She thinks it's fantastic. She's had a couple of honours in the past couple of years, she got an Order of Australia and an Honorary Doctor [of Letters] from the University of Queensland but this is the icing on the cake, it's a permanent thing people will use in Brisbane."
Tour inspires next generation
Budding engineer, Craigslea State High School year 12 student Covey Reyes, said walking through the tunnel was an "amazing" experience.
"We got to talk with engineers, as students, we got to see how it applies to real life, we got to understand how they mitigate environmental factors, how they solve their biggest problems," he said.
"As students, this event was really amazing for us to see because it inspires us and influences us about our future and what technologies we're going to be able to achieve and what projects we're going to be able to create.
"It inspires me to chase that dream even more now because of what I saw today."
The event followed the long tradition of river city residents walking on bridges and through tunnels before they open, including the Clem 7, Captain Cook Bridge, Legacy Way, Gateway and Airport Link.
Engineering enthusiast John Missen, who is turning 75 next week, has now toured the Cross River Rail, Legacy Way, Clem 7 and the Airport Link tunnels.
"It's an engineering feat, probably one of the great seven wonders of Queensland," he said.
"We've just got to keep going, [the] 2032 [Olympic Games] is not far away, 10 years, and we've got to put infrastructure in places, it's got to be all systems go."
'Epic' project for growing region
Cross River Rail delivery authority program director Jeremy Kruger said the walking tour was possible during a window between excavation and concrete being inverted before rail tracks, walkways and other infrastructure were built.
"Within the tunnels, we'll start laying the railway, the tracks, down through the tunnel, we've still got the four underground stations under construction," Mr Kruger said.
"At Roma Street they're doing some of the concrete lining, at Albert Street they've just finished excavation and they're starting to do the reinforced concrete structure.
"At Woolloongabba, we've actually nearly reached ground level, that one is a little bit ahead of the other stations and the concrete structure is now up out of the ground and later this year we'll start the fit-out of the station."
Forty people won a competition on ABC Radio Brisbane to be a part of the experience.
Transport Minister Mark Bailey said the technology and tunnels on display demonstrated the "epic scale" of the project to develop "the first genuine underground rail line in Brisbane history".
"This project is dealing with the growth in south-east Queensland that has been happening and will continue," he said.
"We've got to have a better public transport network and better service and having a new underground line that dissects the CBD that makes the Ekka line a full timetable for the first time, and the Ekka station a full-time station is really exciting."