Sonohyan-utaki Ishimon is a stone gate opposite the stairs that lead up to the Shuri Castle entrance. It is easily overlooked as Shureimon, the main gate to the castle, right next to Sonohyan-utaki Ishimon is more of an eye-catcher. Admission to the gates is free.
The main hall of Shuri Castle was undergoing some renovation i.e. half of the main hall was hidden behind a scaffold. The entrance fee was 800 yen. The fee also gives you access to the excellent museum (English text available). One should know that Shuri Castle is a reconstruction of the original castle which was destroyed in WWII.
Tamaudun: This mausoleum is a short walk west of the Shuri Castle site. For a small entrance fee one gets access to the venue and to a small museum. Note that there are no English descriptions in the museum.
Shikina-en, the royal gardens about 2 km south of the Shuri Castle site, offer an interesting mixture of Japanese layout, Ryûkyûan architecture, and Chinese elements. Don’t expect a fancy Japanese garden. Simplicity prevails.