A building and its former use
Older museum listings describe exhibitions in the town gate. That explains why the name still appears in guides. However, an old exhibition or a surviving weekly schedule does not mean there is still a museum programme inside.
Looking from outside is something else
The gate can be part of a walk through Kampen. Viewing a building from outside does not give access to its interior. Keep that distinction in mind when you plan a route past places that once served as museums.
Look further for exhibitions
If you want to go to Kampen for an exhibition, you can consult the current programme of the Stedelijk Museum. Check the specific address as you do so. A reference to the same museum organisation does not make the Koornmarktspoort an open exhibition venue again.
Before you go
According to the current description, no museum visit is possible in the Koornmarktspoort.
Sources
This information has been compiled from public sources. Not everything has been confirmed by the museum itself; please check opening hours and prices on the museum's website.