Donghae is a working port city on South Korea's east coast, where the Taebaek Mountains press close to the sea. It is not polished like a resort town, and that helps: fishing harbours, rail lines, beaches, caves and mountain valleys all sit within the same compact city.
The coastal sights are the easiest hook. Chuam Chotdaebawi Rock is one of Gangwon's classic sunrise views, while Mukho Lighthouse and the mural lanes below it look over the harbour. Inland, Mureung Valley gives Donghae a stronger mountain identity than its port frontage suggests.
Come with a loose plan rather than a checklist. Donghae is best when you split the day between sea and valley: sunrise at Chuam, a harbour walk around Mukho, then buses or a taxi into Mureung if the weather is clear.