Union Station, designed by Theodore Link, was opened in 1896. The station, train sheds, and power house covered more than 20 acres of what had been the site of Old Mill Creek Pond. The shed is the largest in the United States, and some say that it is the largest in the world. It covered 42 tracks, whose total length came to 18 miles. During its operating peak, the station served 19 railroad companies and 260 trains per day.

The building is two blocks long and includes a hotel. The Terminal Hotel was not part of the original plan, but was added during construction and opened with the terminal in 1896. The waiting room, with a 65 ft. vaulted ceiling, is below street level. It is connected to the Grand Hall above by a staircase which passes under the famous Whisper Arch with a span of 50 ft. Its name comes from the fact that one is able to hear a whisper spoken across it.

The Grand Hall is lighted by stained glass windows depicting the meeting of the East and West. The Hall rises to a vaulted ceiling the height of the building´s peaked roof.

Today, the Terminal is no longer used by passenger trains, but it is served by a Metrolink stop. In 1986, Union Station reopened as a tourist attraction, featuring a mall, restaurants, and clubs. The Terminal Hotel reopened as a Hyatt, and the Grand Hall now serves as the hotel lobby. The shed has been modified to allow more light to enter, and covers a parking area as well as restaurants.