Sleep in Namba or Umeda. The castle is a metro hop. Hiroshima is the next Shinkansen, not a neighbourhood.
Hover a pin on the map for a short preview of each attraction — the same places listed below.
Osaka Castle Umeda Namba & Dotonbori Kuromon Ichiba Shinsekai Hover a pin for a place preview — no separate pages, just the map.
Osaka Castle
Park, moat, keep. Sakura if your dates allow. The interior is optional.
Namba and Dotonbori
The food and neon belt. Stay here if evenings matter.
Kuromon Ichiba
Morning market. Combine with the castle, not with a 9pm kushikatsu crawl on the same stomach.
Umeda and Shinsekai
Sky Building and the station; Tsutenkaku and kushikatsu for old Osaka.