Yosuien is an Edo-period garden near Wakanoura, built for the Kishu Tokugawa lords. Its pond uses seawater, which gives the garden a different feeling from the inland strolling gardens more common around Kyoto and Nara.
It is a calm, compact stop rather than a blockbuster. Visit it with Wakanoura and Kishu Toshogu if you want the quieter historic side of Wakayama.