The ruins of the castle Kaja are located to the north of the village Merkersdorf, which is now part of Hardegg, a small border town on the Austrian side of National Park Thayatal. The ruin of the castle towers over the Austrian-Czech border river Thaya in the Waldviertel region. The visit may be well combined with a visit to the nearby Czech castle Novy Hradek at Lukov, which is in the beeline just 2 km away, the hiking trail is 17 km long.
