Castle Stalker () is a four-storey tower house or keep picturesquely set on a tidal islet on Loch Laich, an inlet off Loch Linnhe. It is about north-east of Port Appin, Argyll, Scotland, and is visible from the A828 road about midway between Oban and Glen Coe. The islet is accessible (with difficulty) from the shore at low tide. The name "Stalker" comes from the Gaelic "Stalcaire", meaning "hunter" or "falconer". The island castle is one of the best-preserved medieval tower-houses to survive in western Scotland and is a Category A listed building. It stands in the Lynn of Lorn National Scenic Area, one of forty such areas in Scotland.