A behind the scenes tour of the GPO is one of 200 events taking place this week as part of the capital's annual festival of architecture, which gives people the opportunity to visit areas not normally open to the public.
Open House Dublin, which is in its 20th year, says it aims to show how design is important to everyday lives.
The tour of the GPO comes at a time when the future of the building is at the centre of a debate about how to improve Dublin's O'Connell Street.
The site, which played a key role in the 1916 Rising, was shelled and gutted by fire during the rebellion but was rebuilt and reopened in 1929.
Since then, it has been home to RTÉ, the Department of Posts and Telegraphs, and the headquarters of An Post - with around 2,000 staff working in the building at its peak.
But for the past two years, since An Post moved to a new HQ close to Dublin Port, most of the building has been unoccupied with only around 180 staff, including those manning the remaining post office and museum, remaining.
The bowels of Dublin's most famous building contain tunnels and vaults dating back to the origins of the building alongside numerous art deco and modernist features that show the many uses the building has had in modern times.
Historian Dr Caitlin White, who will guide tours of the GPO during the festival, said people are often taken aback by the scale and the behind the scenes use of the country's most famous building.
She said: "When we come in, you really get a sense of the different eras that are encapsulated here in the GPO, from Georgian to more modernist settings.
"You also move through from a very ceremonial, a very ornate part of the GPO to the part that's actually used every day by people here in their jobs and it's very functional."
Dr White said that when "many people" visualise the "really iconic front image" when thinking of the GPO.
"But if you're walking down Henry Street, if you look up, you'll actually see how far back the GPO extends," she said.
"It's a massive site right here in Dublin city centre," she added.
She noted there is a "social history" as well about the lives of some of the people who lived and worked in the building in the 19th century.
"Many of the workers actually lived here on site," she said.
"In 1828 there was 28 postal staff who lived in the GPO as well as the secretary of the post and three other families, along with all the domestic servants, the housekeepers who all lived here in the building," she added.
Dr White said the "moments that shaped the nation's history" happened at the site.
"When they reopened it in 1929, the designer made sure that it didn't just belong to the people of Dublin, but actually belongs to the nation," she said.
"They used stones from all four provinces in the rebuilding of the GPO to represent the belonging to the nation that this building has," she added.
The theme of this year's Open House Dublin festival is 'Future Heritage'.
Emmett Scanlon, Director of the Irish Architecture Foundation, said the discussions around the GPOs future are central to that theme.
He said: "It's an opportunity to think about our past and our heritage and our built heritage, the stories that are contained within our built environment.
"But also to look forward to the future and say 'what are we going to do next? How are we going to take care of the buildings and places that we have? And how do we have conversations about what might be appropriate and what might suit everybody in society going into the future?'"
Mr Scanlon said there is "something really powerful" about that idea that "we are taking care of this great building which has our history".
"The challenge for us now as a nation and as a people is to think how do we hold on to that history, protect it," he said.
"But also look forward to the future and use this great resource? Because the best buildings we have are the ones that are already built," he added.
He added: "What we need to do is bring people along with us, the local community, the residents, the people who invest every day in their lives in this place."
Mr Scanlon said the plan "should think about the everyday but then we also need to think much longer term".
"Where do we want to be in 100 years with the street? Who do we want to be living on it? What kind of resources do we want here? What culture? What places for our young people into the future?"
A tour looking at O'Connell Street’s untapped potential also forms part of this year’s programme of 200 events.
Historian Donal Fallon said the street is full of social history and he believes any future development of the street should focus on the people who live and work there rather than the tourists that visit it.
He said: "There's a lot of nostalgia in this street.
"Shop fronts are really beautiful. We don't think about shop fronts as part of the architectural landscape of a city, but they are.
"I love the neon signage on McDowell's Happy Ring House, it's in business so long it was looted during the 1916 Rising.
"Over Footlocker we have the Confectioners Hall, what was Lemon Sweets - another beautiful sign that's slowly falling away.
"Little things like that are very important social history, the place that our grandparents and great grandparents shopped."
Mr Fallon said it is "a beautiful street of set piece architecture".
"It's a street that has been at the heart of Irish history, especially political history, and I think it's a street that we have to be positive about going forwards," he said.
"For me, I think cities have to prioritise those who live in them and cities that put tourism ahead of the needs and concerns of those who live there, they miss something very fundamental."
He said tourism is "often motivated by the desire for something authentic".
"When we go abroad, we want to do what the locals do, how they do it," he said.
"So there's great potential in streets like this to think about how do we get people back into town? How do we make coming into O'Connell Street something that we do?"
The Open House festival runs from 11 to 19 October.
