It's been dirty work scraping more than 10 tonnes of pigeon poo from the dome of one of Melbourne's most iconic buildings.

But after a “painstaking” clean, the iconic dome atop Flinders Street Station has been restored for the first time in more than 100 years.

The high dome ceiling, built in 1910, was rejuvenated as part of a $100 million upgrade designed to bring the city’s busiest station back to its former glory.

Only a handful of people have ever seen inside it, and on Monday, Public Transport Minister Jacinta Allan was among them as she climbed inside the “symbolic” feature of Melbourne’s busiest train station to view the work up close.

“It’s a big job to restore the history and the grandeur of this magnificent building,” she told reporters on Monday.

“Indeed, it is the international symbol of Melbourne.”

The work revealed links to the dome’s original builders, who penned their names into the dome. A pair of spare flag poles were also left inside.

Scaffolding on the station facade will be removed by mid-year, while the building is painted to its original colours.

A new entrance to platform 10, connecting it to Southbank, will be finished at the end of April.

The station ballroom is also being water-proofed and stabilised for future use as part of the upgrade, to be finished by the year’s end.

Ms Allan would not say what the ballroom and other spaces will be used for, other than it needed to be “sympathetic” to the movement of 200,000 Victorians who use the station daily.

By Christine McGinn