The cars were painted a distinctive night-blue hue once associated with the Orient Express, the famed long-distance trans-Europe passenger train synonymous with 20th century travel glamor.
While the train immortalized by crime author Agatha Christie no longer exists, luxury travel company Belmond operates an Orient Express homage between London and Amsterdam, and hotel group Accor is launching an Italy-based service under the same name in 2023.
Mettetal wasn't just a railway fan, he was working on a PhD on the history of the Orient Express. His research involved trying to ascertain how many original Orient Express train carriages still exist today, where they were located, who owned them and what condition they were in.
He knew some vintage carriages were in service -- like those that operate the Belmond Orient Express route -- and others were on show in museums. But he figured many of the cars were scattered across the globe, forgotten.
Mettetal spent most of 2015 hunting these abandoned carriages, scrolling through archives, talking to railway fans on message boards and combing through online videos. Every so often, he'd spot a clue that looked promising, like the blue carriages in the YouTube video.
Mettetal hit pause on the video and examined the frame closer. The video had been uploaded anonymously and there wasn't much accompanying information. But it was just possible to make out the name of a station on the screenshot: Małaszewicze.
Through Google, Mettetal discovered there were several places in Poland named Małaszewicze. He looked each spot up on Google Maps, switching to 3D view and zooming in, searching for the distinctive blue carriages with their white roofs.
And then, bingo, he found what he was looking for: a 13-carriage train that looked suspiciously like the Orient Express, parked up at a Małaszewicze station on the border between Poland and Belarus.
Speaking to CNN Travel today, Mettetal says this was a "magical" moment.
"Thirteen cars in one go!" he exclaims. "It's like discovering a treasure."