Kadı Kalesi, also known as Anaia, is the archaeological counterweight to Kuşadası's beaches and cruise traffic. The site preserves a Byzantine castle on a low hill by the coast, in a place associated with the old port of Anaia and its role in Aegean trade. Excavations have revealed layers far older and more complicated than the surviving walls suggest at first glance.
Access and interpretation can vary, so treat it as a serious ruin rather than a polished visitor attraction. The reward is context: from here the Samos Strait, the coast road, and the maritime logic of Kuşadası make much more sense. Go in cooler hours, as shade is limited.