People can catch a glimpse of where significant decisions were made during the first Dail 100 years ago.
The Lord Mayor of Dublin is inviting people to come into the Mansion House from 10 o'clock this morning until 5pm.
A new exhibition on the revolutionary period is also on display, with a huge amount of other memorabilia.
Lord Mayor Nial Ring says it's already attracted huge crowds ahead of the anniversary tomorrow, with nearly 4,000 coming through the door yesterday and Friday.
"The Mansion House had a pivotal place in Irish history," he said.
"The first Dáil, tomorrow is the 100th anniversary... it's important that people know exactly what happened here.
