As Great Central Station, Randolph Street terminal, along with Van Buren Street a few blocks south, was IC's primary downtown Chicago terminal until the completion in 1893 of Central Station (closed 1972) just south of Grant Park at today's Roosevelt Road. It still received many trains thereafter, but was of secondary importance. Its importance increased dramatically in 1926 with the electrification of commuter services on IC's main line and its Blue Island and South Chicago branches. Commuter trains from all three branches were now routed into the Randolph Street terminal, while intercity traffic continued to terminate at Central Station.
Originally, the station platforms were exposed and the ticketing facilities and the waiting room were located in the attached facility. The construction of Millennium Park gradually placed the entire station "underground." Millennium Station existed in a state of perpetual construction from the mid-1980s until 2005: exposed steel girders covered in flame retardant, unpainted plywood walls, bare concrete floors, and dim utility lights created a notoriously unfriendly, cave-like environment. Skidmore, Owings and Merrill was the architect for the station redesign.
Millennium Station serves as a nexus of several Chicago Pedway connections, which links it to several hotels, residential buildings, office buildings, "L" stations and other notable locations. The pedway itself hosts a number of shops, eateries and services. While some portions of the system remain open at all hours, most of them close by 7:00 PM on weekdays and 6:00 PM on the weekends, rendering a significant portion of the system unusable during non-business hours.