Doe Castle stands on a small promontory above Sheephaven Bay, a compact 15th-century stronghold tied to the MacSweeney clan. Its restored tower and waterfront setting make it one of the more atmospheric castle stops in northern Donegal.
It is not a huge ruin, so treat it as a scenic detour rather than a half-day sight. The reward is the combination of stonework, sea inlet, and Donegal weather moving fast across the bay.