Ilse van Ewijk
Google
The park itself is free, including the steep walkway up to the castle (somehow it makes me miss staircases). You only pay to go into the castle, which is also where all the stamps are. The castle itself is small, but the park, the surrounding walls and the gates make for a great experience. Be mindful of the closing time though, as it is fairly early.
There's a free parking lot where the museum is (but it was closed today, sadly). Although the parking lot was almost full when I arrived, there was no sign of any tour buses. So I still got an overall quiet experience, which was much appreciated.
Don't forget to visit the little gift shop at the bottom of the uphill walkway, as they have a cute little fan shop, as well as some Yadon/Slowpoke merch (mascot of the prefecture).