Omaha's Union Station closed in 1971 and reopened in 1997 as The Durham Museum. The National Park Service says "the station is one of the best examples of art deco architecture in the country."
The museum has permanent exhibits that explore the region's history, as well as variety of temporary exhibits. The current exhibit is Hall of Heroes (until April 16, 2023), which my kids really enjoyed but it was incredibly busy during our Saturday morning visit. I don't know if that's typical for a Saturday or is due to the popularity of the current exhibit.
There was a long line of people waiting to enter when we arrived, but the line moved fairly quickly. I booked tickets online in case there was a shorter prepaid line, but everyone waits in the same line. Admission is $13 for adults and $7 for kids.
They have a free 2-level parking deck with easy access to the museum. The museum opened at 10 am and the parking was half full by 10:15 am. When we left at noon, it was completely full and people were circling for spots.