Grand Central Terminal isn’t just a pretty face, with its distinctive architecture and interior design earning it many design accolades over the years. Spread over 49 acres, with 44 platforms and 67 tracks on two levels, it’s also the world's largest train station by number of platforms and area occupied.

Designed and built from 1903-1913, the National Historic Landmark and Guilded Age Monument, located at 42nd Street and Park Avenue in Midtown Manhattan, New York City, is no stranger to the limelight and is the 10th most visited tourist attraction globally (with 21.6m visitors in 2018 excluding train and subway passengers). It also boasts a library, event hall, tennis club, control center, and office, and according to @DannyBoyBronx on Twitter, a dirty little secret on its ceiling.

Read more: 'I took DNA test for a laugh - and accidentally uncovered my mum's devious past'

For all the latest on news, politics, sports, and showbiz from the USA, go to The Mirror US.

Designed with a stunning celestial mural of constellations painted in 1913 on a navy blue background (with astronomers and 50 painting assistants working on the design), by the 1980s the ceiling was obscured by decades of grime, soot and cigarette smoke.

According to Danny, if you look up towards the ceiling stars and crab constellation on track 30, you’ll notice a sign of this grime: “When they redid the concourse over in Grand Central Station, they left a little square patch on the ceiling to show you just how dirty the ceiling was from all the diesel smoke. Go by track 30 look up and to the West, you’ll see the patch,” he says.