First built in the 1580s on the order of Toyotomi Hideyoshi, Osaka Castle was the largest castle in Japan, a magnificent structure used by Toyotomi as a military stronghold from which to wage war against rebellious feudal lords in far-flung provinces. By the time he died in 1598, Toyotomi had accomplished what no man had done before: crushed his enemies and unified all of Japan under his command.
After Toyotomi's death, Tokugawa Ieyasu seized power and established his shogunate government in Edo. But Toyotomi's heirs had ideas of their own: Considering Osaka Castle impregnable, they plotted to overthrow the Tokugawa government. In 1615, Tokugawa sent troops to Osaka where they not only annihilated the Toyotomi insurrectionists but destroyed Osaka Castle. The Tokugawas rebuilt the castle in 1629, but the main tower was destroyed by lightning 36 years later, and the rest burned in 1868 as the shogunate made their last stand against imperial forces in what later became known as the Meiji Restoration.
The present Osaka Castle dates from 1931 and was extensively renovated in 1997. Built of ferroconcrete, it's not as massive as the original but is still one of Japan's most famous castles and is impressive with its massive stone walls, black and gold-leaf trim, and copper roof. Its eight-story donjon (keep) rises 39m (130 ft.), with a top-floor observatory offering bird's-eye views of the city. The rest of the donjon houses a museum that uses videos, holograms, models, and artifacts to describe the life and times of Toyotomi Hideyoshi and history of the castle. Unfortunately, most explanations are in Japanese only, but there's plenty to see, including a folding screen with scenes of the intense fighting that took place between Toyotomi and Tokugawa forces, samurai armor and gear, a full-scale reproduction of Toyotomi's Gold Tea Room, and a model of Osaka Castle during the Toyotomi Era. If you want, you can have your photo taken in period clothing for ¥300. Plan on about 45 minutes here.