If you like to railfan, you might want to come down here sometime. The Sioux Falls Freight Yard usally has 2 BNSF switchers operating daily to move cars around, You might also catch one of the locals headed to Garretson or somewhere else on the Marshall Sub. But be careful, Downtown can be a little scary at night, and PLEASE stay off the tracks!! The yard also sees a few D&I and Ellis and Eastern Shortline locals from time to time. The yard office is an ex-Great Northern depot, and is a really cool building.
If you go downtown, you'll find about four to five old train depots and several other restored railroad buildings. Only the Great Northern Depot is still used by the Railroad, the others have been converted to office and retail use. At one time Sioux Falls had 5 railroads, which explains all the structures. You'll also find a few old railroad bridges around town, some are now part of the bike trail. The depot in the picture is now the homeland security office and is located downtown next to the Country Inn and Suites.
The second picture is of the Great Northern Depot that is now a BNSF office at the railyard downtown. (to see it, click -more photos) For more info on the railyard, I have a "off the beaten path" page on it too.