Up to 10,000 people will be able to walk a 600m round trip of the twin tunnels next month.
"Our priority is ensuring everyone is safe and has an enjoyable time when they visit us," said CRL chief executive Sean Sweeney.
"While the walk won't take long - about half an hour all up - people should be aware that there are some skinny bits underground where the walking routes narrow and areas where lighting is limited that may not suit people uncomfortable in enclosed spaces," he said.
Tunnel tickets will be restricted to 1000 people per hour. Sweeney said there may be some queuing before people can start the walk.
The tours will start at 8am and last entry will be 5pm. Entry and exit points will be via the Britomart Station in lower Queen St.
Open days at the 2.4km Waterview Connection twin-tunnel motorway project drew tens of thousands of people. In 2017 just before it opened, around 42,000 people booked an open day visit.
CRL asked people how keen they would be.
"Me!" wrote an enthusiastic Auckland councillor Cathy Casey.
People remembered the Victoria Park motorway tunnel project and its open day, including a sit-down black-tie dinner before the cars flowed.
Families expressed enthusiasm to see inside CRL, one vowing to travel from Wellington on the Northern Explorer train to go underground.
"Great idea but you will need to allow plenty of opportunity and allocated ticketing, as there will be huge interest, as gauged by the Waterview tunnel experience," said one follower, encouraging the business to avoid disappointing those interested.
Others asked for money to be charged, saying that could support charities. "This is a once-in-a-lifetime experience," said another follower.
