Sopron's castle survives less as a single romantic ruin than as a set of walls, gates, and defensive fragments built into the fabric of the old town. That makes it easy to miss if you arrive looking for towers and battlements, but rewarding if you like cities where the medieval plan is still readable.
Walk slowly around the inner ring near the Firewatch Tower and Fő Tér, watching how later houses reuse older stonework. The remains help explain Sopron's compact, enclosed feel: this was a border town that took its walls seriously.