Visitors to Lincoln Castle have a rare opportunity to see inside the former Victorian prison featured in the TV drama series Downton Abbey.
The male prison, which is not open to the public, stood in for York Prison where Downtown Abbey character John Bates is serving time for murder.
After the events, the prison will be closed until 2015 for refurbishments.
The work is part of a £20m scheme, which will also see the creation of a purpose-built Magna Carta centre.
The prison is open as part of Lincoln's heritage events this weekend.
Other improvements at the castle will include repairs to its walls to allow visitors to walk all the way around the perimeter.
Lincoln Castle was built in 1068 and has housed the Magna Carta since 1215, which is one of only a handful of surviving originals.
It is hoped the work will be completed in time for the Magna Carta's 800th anniversary in 2015.