Beneath the streets of New York City lies the skeleton of one of the most ambitious communication systems in U.S. history: a 27-mile pneumatic mail network that once moved 100,000 letters a day—using nothing but air pressure. From 1897 to 1953, steel canisters shot through underground tubes at 35 miles per hour, connecting 23 post offices across Manhattan and Brooklyn. It was fast, reliable, and nearly invisible to the public.

So why did this futuristic mail system vanish? And how did something so ahead of its time become obsolete in just a few decades? In this episode, we explore the rise and fall of New York’s pneumatic mail system—from ceremonial cat launches and same-day Wall Street contracts to deadly tube explosions and sandwich deliveries gone rogue. Plus: what’s still down there today.