Can I go to this museum without a tour can I just walk around myself?

They also have a walking tour available with an audio guide I think

The Museum is free of cost but suggested donation. They offer an excellent 75 minute walking tour.

Yes. If you want to just walk around the Inn you can but you won't be able to go into certain places that the tour would allow you to do so. The museum is also free to walk around in and is inside the gift shop.