Okazaki Castle is the city's anchor and the place to start. The keep is reconstructed, but the site matters: Tokugawa Ieyasu was born here, and the surrounding park holds museums, shrines, statues, and seasonal gardens that turn the history into a pleasant half-day walk.
Spring is the famous moment, when cherry trees line the castle park and riverbanks. Outside that season, the museum displays and fifth-floor view still make the castle the clearest introduction to Okazaki.