Senua, also written Senoa, is a small island off Sepempang village on the east side of Great Natuna. It is one of the better short boat trips from the main island, with coral for snorkeling, a small cave, and the chance of seeing the endemic Natuna Island surili, locally called kekah.
Treat it as a nature stop rather than a beach club. Bring water, reef-safe sun protection, and enough cash for the boat, and check sea conditions before committing.