St. Louis Union Station, designated a National Historic Landmark in 1970, is a former passenger train terminal in St. Louis, Missouri. Once the world's largest and busiest train station, it was converted in the early 1980s into a luxury hotel, shopping center, and entertainment complex. Today, it is one of the city's major tourist attractions.

In 1889, the Terminal Railroad Association was formed to consolidate the numerous railway entries and exits in the St. Louis area by building a new Union Station. St. Louis architect and former railroader, Theodore C. Link, was chosen to design the station. His design included three main areas: the Headhouse, the Midway and the Train Shed. The station is modeled after Carcassone, a walled, medieval city in southern France with a mix of Romanesque styles. The interior and exterior details are a combination of both Richardsonian Romanesque tradition and French Romanesque or Norman style. These designs are most evident when entering the Station's Headhouse. The Grand Hall features with sweeping Romanesque archways, a 65-foot barrel-vaulted ceiling, fresco and gold leaf detailing, scagliola surfaces, mosaics, and stained glass windows. The Headhouse and Midway are constructed of Indiana limestone and originally housed a hotel, a restaurant, passenger waiting rooms and railroad ticketing offices.

The Midway is a 610-foot-long and 70-foot-wide concourse that connected the Headhouse to the Train Shed. The Midway was constructed with a light steel trussed roof of glass and iron. The Train Shed was the largest single-span train shed ever constructed. Measuring 11.5 acres under sweeping arches, it once covered the greatest number of train tracks (32) than any other station in the nation. Measuring 606 feet wide by 810 feet long, the Victorian-engineered shed soars to 140 feet with its massive space divided by five structural bays.

When the station opened on September 1, 1894 and cost $6.5 million to build. At the time it was the world's largest and busiest railroad station and its train shed was the largest roof span in the world. In 1903, the station was expanded to accommodate visitors to the 1904 St. Louis World's Fair. In 1903, the station was expanded to accommodate visitors to the 1904 St. Louis World's Fair. At its height, the station combined the St. Louis passenger services of 22 railroads.

In the 1940s, it handled 100,000 passengers a day. The famous photograph of Harry S. Truman holding aloft the erroneous Chicago Tribune headline, "Dewey Defeats Truman," was shot at St. Louis Union Station as Truman headed back to Washington D.C. After World War II the demand for railroad passenger services declined due to the rise in popularity of the automobile and the construction of the Interstate System. When Amtrak took over national rail passenger service in 1971, trains leaving St. Louis Union Station were reduced to only three a day. In 1978 the last train left St. Louis Union Station and Amtrak began using a small building two blocks east of Union Station.

In 1985, after a 150 million extensive renovation, St. Louis Union Station celebrated its grand reopening as the largest adaptive re-use project in the United States featuring unique and exciting shops, restaurants, entertainment venues, and a hotel complex in the Headhouse. The train shed also houses a lake complete with paddleboats available for rent. Across from Union Station is Aloe Plaza with the magnificent Carl Milles' Fountain featuring elaborate bronze sculptural pieces representing the meeting of the rivers.