During Union Station's boom years in the 1940s, more than 300 trains arrived or departed daily and 100,000 passengers passed through the terminal. These days, about 50,000 commuters scurry through Chicago's most magnificent transportation terminal every day. Unless you enter Union Station on the west side of Canal Street, it's entirely possible to buy your tickets and board your train without ever seeing the Great Hall, the surviving half of the original 1925 station. Take a few extra minutes, though, to take it in. The pink Tennessee marble floors harmonize with the marble walls, Corinthian columns and bronze floor torches. The soft light filtering through the Great Hall's vaulted skylight immediately puts you at ease. The room's size tends to hush people, so its long wooden benches are a good place to relax, admire the architecture, or just daydream.   "The Untouchables" was filmed here in 1987.   Commuting tips Here are some hints on how to get through the station with a minimum of fuss. Amtrak General information on nationwide train service. Food You can find everything from Corner Bakery to Connie's Pizza at the food court. Convenience Shops These stores are a great way to kill time. Station Diagram. Use this map to find your way around the station. By John Gerard McLaughlin Photos: Steel Bokhof