Yes, there is a National Mustard Museum! Located in the western suburbs (and relocated from the far western suburbs), it is more everything-that-is-mustard-you-can-buy than an actual museum. The actual museum is located in the basement and is free. A little disappointing, but really, what can someone expect from a mustard museum! Still, if you have a mustard fanatic in the traveling group it is well worth the drive. The highlight is the very large gift shop full of mustard-related items. It even has a tasting bar! Expect to leave with at least a postcard of the in-on-the-joke owner. I ended up with a few bottles!
7477 Hubbard Avenue, Middleton, WI 53562