Near Castle Douglas, Threave is a Black Douglas island tower house on the River Dee. You park, walk about 15 minutes to the jetty, then cross by passenger boat — the setting does half the work before you even step inside.
Seasonal site (Historic Environment Scotland): typically open 1 Apr–30 Sep daily 10:00–16:00, 1 Oct–31 Oct to 15:30, closed Nov–Mar. Reduced admission around £4.50 adult / £3.50 concession / £2.50 child; members free. Address for the approach: Castle Douglas, DG7 1TJ.
Full guide, photos and visit tips:
https://castlescotland.app/threave-castle/
— Castle Scotland