There is free and paid parking at the entrance, entrance to the park area is free, you can just walk, you can rent bicycles, there is a Playground. The entrance to the castle is also free, you can take beautiful photos, consider the facade of the courtyard. Only museum visits, exhibitions and excursions are paid. The castle itself is beautiful, restored, looks atmospheric, the architecture is fascinating.
A beautiful castle that is definitely worth a visit. I advise you not to take a full visit to the museum. Take only 3 main halls. Additional halls are very steep ascents and descents that not everyone can handle)
In my opinion, all these crafts in the Gromyko Park are low—art hack work. It causes a feeling of "Spanish shame" — a cringe in front of the guests of the city...