One Chicago dished out one of its biggest disasters to date in its 2025 crossover. There was a huge explosion, victims trapped under rubble, and an entire train full of passengers who were under threat of having concrete structures collapse on them. It was a tense experience for all involved.

In typical One Chicago fashion, characters came up with clever and often genius methods to save lives and ensure the people responsible for the explosion were brought to justice. One aspect of the three-part story that may have taken some viewers aback, however, were Al Capone's secret tunnels. They were repeatedly referenced throughout, and proved to be play a pivotal role in the plot. So what is the deal? Are these tunnels real?

The Chicago tunnels are over 100 years old Chicago P.D. -- "In The Trenches: Part III" Episode 12014 -- Pictured: Miranda Rae Mayo as Stella Kidd -- (Photo...