When St. Louis Union Station opened on September 1, 1894, it was the largest train station in the world, designed by Theodore Link in a Romanesque Revival style that borrowed from the walled city of Carcassonne in southern France. The Grand Hall was the building's centerpiece -- a cavernous room with a 65-foot barrel-vaulted ceiling covered in ornamental plasterwork, stained glass windows, and allegorical paintings. Thirty-two railroad tracks fanned out behind the headhouse under a massive train shed designed by George H. Pegram, the largest single-span train shed ever built at the time. The station served as the hub for 22 railroad companies, and its Whispering Arch -- a Romanesque archway near the Grand Hall entrance where whispers carry from one end to the other -- became a beloved curiosity for generations of travelers.

St. Louis Union Station reached its peak during World War II, when the station processed over 100,000 passengers daily. Servicemen and women shipped out through its concourses. Families crowded the platforms for tearful goodbyes and joyful reunions. The station was not merely a transit point but a social crossroads where all of America passed through. During the 1940s, St. Louis was the nation's railroad hub -- more lines converged here than at any other city. The Truman photograph in 1948 captured a president at the peak of his improbable victory, but it also captured the station at the peak of its relevance. Within two decades, the interstates and jet aircraft would render the great train stations obsolete.

The last regularly scheduled train departed St. Louis Union Station on October 31, 1978. Amtrak had consolidated its operations at a smaller facility, and the grand building fell quiet. The train shed, once the busiest covered space in America, stood empty. The Grand Hall gathered dust. For several years, the station's future was uncertain -- demolition was discussed. But the building had been designated a National Historic Landmark in 1970, and preservationists fought to save it. In 1985, a $150 million restoration transformed the station into a hotel and shopping complex. The Hyatt Regency St. Louis opened in the renovated headhouse, and the train shed was converted into a festival marketplace. The restoration preserved Link's architectural details while giving the building a new economic purpose.

The latest reinvention of St. Louis Union Station has turned it into something entirely unexpected. The St. Louis Aquarium at Union Station, which opened in 2019, spans 120,000 square feet with over 1 million gallons of water and houses 13,000 animals, including sharks, rays, and river otters. A 200-foot observation wheel rises beside the train shed. A miniature golf course winds through the former platform areas. A fire-and-light show plays nightly over a lake beneath the train shed's historic steel framework. The Grand Hall still anchors the complex, its barrel-vaulted ceiling now illuminated by a 3D light show that transforms the ornamental plasterwork into a moving canvas. It is a strange second life for a building designed to move people across continents -- but Theodore Link's architecture endures, its grandeur intact beneath the aquarium tanks and neon lights.