Can I add Castle Caulfield to a car journey through the Dungannon area?

Yes.

Castle Caulfield is a historic ruin in Castlecaulfield village, with on-site parking and free access listed by Discover Northern Ireland. It is worth treating as a separate stop rather than expecting it to be visible from a through road. Navigate to Castle Grove, Castlecaulfield, BT70 3NL and follow local signs once you enter the village. The attraction is primarily an outdoor historic structure, so plan around daylight and weather rather than assuming indoor visitor facilities or a staffed car park.