Unstan (or Onstan, or Onston) is a Neolithic chambered cairn located about 2 miles (3 km) north-east of Stromness on Mainland, Orkney, Scotland. The tomb was built on a promontory that extends into the Loch of Stenness near the settlement of Howe. Unstan is notable as an atypical hybrid of the two main types of chambered cairn found on Orkney, and as the location of the first discovery of a type of pottery that now bears the name of the tomb.