Träby castle lies out on the Stora Alvaret, 700 meters north of Träby. The castle is one of the islands most peculiar castles.
The castle is made out of three incorporated ring castles. The three ring castle's inner diameter varies between 44 and 66 meters. The walls are partly in ruins, best preserved is the brickwork in the middle. The foundation, which is inside the walls, is today barely seen. When Rhezelius visited the castle in 1634 the foundation was distinct and he could count to 30 foundations in the northeast castle ring, 32 in the middle one and 14 in the southwest. The southwest castle lies in ruins after a homestead, Christineborg, which happened in the beginning of the 1800s. After a couple of meters southeast from the castle is a grave field with almost 10 visible round stone settings.