Sønderborg Castle is located in the town of Sønderborg, Denmark on the island of Als in South Jutland. It houses a museum focusing on the history and culture of the area. The castle is located in the middle of the town, in a park setting overlooking Als Fjord. The museum is open year-round.

Sønderborg is a Danish town in the Region of Southern Denmark. It is the main town and the administrative seat of Sønderborg Municipality (Kommune). The town has a population of 28,137, in a municipality of 74,380. In recent times, Sønderborg is a center for trade, tourism, industry, and education in the region of Southern Denmark. The town is the headquarters for several industrial companies. Sønderburg joined the UNESCO Global Network of Learning Cities in 2016.