Kobe — harbour views and wagyu
Kobe sits roughly 20-30 minutes from Osaka on JR, Hanshin or Hankyu lines, and its history as one of Japan's first ports opened to foreign trade in the 19th century still shows in its harbour views, Chinatown and a scattering of Western-style buildings on the hillside. It's also, unsurprisingly, one of the best places in the country to eat genuine Kobe beef.
Himeji Castle
Himeji, another 30-40 minutes past Kobe, holds Himeji Castle — nicknamed the White Heron Castle for its bright, wing-like white walls — widely considered the best-preserved original castle structure in Japan and a UNESCO World Heritage Site. Unlike Osaka Castle's concrete reconstruction, most of Himeji's structure is original, and the interior wooden staircases and defensive layout are still intact to walk through.
Combining the two
Kobe and Himeji sit on the same rail corridor west of Osaka, so a single long day can realistically cover a few hours in each — Himeji Castle in the morning while it's cooler and quieter, Kobe's harbourfront for an evening meal on the way back.
Himeji Castle's interior involves steep traditional wooden stairs and no elevator access. It's a physically active visit — worth knowing if mobility is a concern.