Nice park away from busy streets of the city and you can avoid tourists pouring to the castle by staying outside inner wall. Walking around the castle is very relaxing.
It is relaxing to walk around, the train station and the castle are in the park. You can see the sakuratrees along the riverside with a wonderful view in april
It's a nice park with lots of different spaces. The grilled crab surimi from the food truck near the castle was surprisingly good--fluffy and bouncy with a nice sweetness.
When strolling through this park, you actually don't think you're in a big city as Osaka. Relaxation can be easily achieved here. Note that it's quite touristy and might be crowded with Chinese.