Beneath Toronto’s bustling streets lies a hidden world most people never see — over 3,400 miles of tunnels, storm drains, and pumping stations that carry water where rivers once flowed. In this episode, we uncover how Toronto transformed its natural creeks and valleys into one of the largest underground sewer networks in North America.From lost waterways like Garrison and Taddle Creek to the engineering mega-projects that reshaped the city, this story reveals how politics, public health crises, and rapid growth buried Toronto’s rivers forever. What was once open water now flows in darkness — a hidden layer of the city’s forgotten history.

Deep in California’s high desert, row after row of U.S. Army tanks, Humvees, and armored carriers sit baking in the sun. More than 20,000 vehicles, lined up like a mechanical graveyard, stretch across 36,000 acres of barren land. To the outside world, it appears to be mass abandonment—but the truth is far more complex.In this episode, we uncover the hidden history of Sierra Army Depot, the Army’s vast storage site for America’s war machines. From its World War II origins to the Cold War buildup and its modern role as both scrapyard and lifeline for the military, this is the story of how and why California became home to the largest tank depot in the United States.

Beneath the quiet town of Wieliczka, Poland, lies one of the most extraordinary underground creations in human history. Stretching for over 180 miles, the Wieliczka Salt Mine holds chapels carved entirely from salt, a vast cathedral, and even an underground lake once sailed upon by visitors. For centuries, it has drawn kings, scientists, and artists into its shadowy depths.But not everything has remained on display. Sealed-off shafts, hidden monuments, and forgotten sculptures have been rediscovered in recent decades—remnants of a working mine that also became a place of faith, devotion, and artistry. From the world’s largest underground chapel to a forgotten salt obelisk for an emperor, this is the story of the Wieliczka Salt Mine’s lost wonders and why they still captivate today.