Posterngate, a Roman gateway lying beneath the Royal Bank of Scotland in Bank Street, will open to visitors for one day this summer.
To help preserve this part of the Lincoln’s heritage, Posterngate remains closed for most of the year.
However, the site will open on Tuesday 23 August between 10am and 4pm. Entry costs 50p per person and under 5s are free.
Tours last for 15 minutes and include a historical talk and a chance to take photographs.
There are also information boards for people to find out more about Lincoln during Roman times.
Sally Bleasdale, The Collection’s Access Officer, said: “The site was discovered during excavations in the 1970s and has remained popular with visitors ever since.
“Posterngate itself was a gateway that allowed people to access boats on Lincoln’s waterfront.
“It is widely thought that the route was used by merchants and traders when Lincoln’s waterside was a bustling port.
“Visitors can also see a Roman limestone wall, which used to form part of the main Southern Wall of the old city.”