Only the seriously imposing walls of the original Obi-jō are intact, but the grounds and surrounding area host several important buildings, including the painstakingly reconstructed Ōte-mon gate; Matsuo-no-maru, the lord's private residence; and the Obi Clan Historical Museum, showcasing artefacts from art to armour. Beautiful Yōshōkan, formerly the residence of the clan's chief retainer, stands just outside the castle entrance and has a large garden with Atago-san (Mt Atago) as striking 'borrowed scenery'.
Exhibits are almost all in Japanese only, so unless you have a Japanese speaker in tow you'll need to appreciate them for their intrinsic beauty.