Raet National Park extends along the coastline north and south of Grimstad, covering 607 square kilometres of coastal nature and sea. The park protects the distinctive ra landscape — the underwater ridge and associated islands formed by glacial activity at the end of the last ice age. The result is a sheltered inner archipelago of small islands, skerries, and protected bays that provide some of the best swimming and small-boat sailing on the Norwegian south coast.
The islands of Store and Lille Hampholmen, accessible by boat from Grimstad harbour, have secluded sandy beaches and clear water. Marivold is a peninsula with camping. The park has no visitor centre in Grimstad itself, but the national park information is available at the tourist office near the harbour.