Ko Samet sits entirely within Khao Laem Ya–Mu Ko Samet National Park, which covers the island and several smaller uninhabited islands to the south. The national park status is the reason the interior forest has been largely preserved — the hills in the centre of the island are covered in deciduous tropical forest, and the designated park areas on the uninhabited southern tip are left wild.
You pay the park entrance fee (200 baht for foreign visitors as of 2024) when you arrive at Na Dan pier — rangers check tickets on the way into the main beaches. The fee goes toward maintenance of the park's trails and beaches. The forest interior is accessible on foot via tracks from the main road; bring water and watch for monitor lizards and the occasional sea eagle overhead.