Constructed in 1537 atop a bluff overlooking the Kiso River, this four-story donjon -- much smaller than most of Japan's castles -- is Japan's oldest and is a designated National Treasure. It miraculously survived centuries of earthquakes (part of it was damaged by an 1891 earthquake but then repaired) and wars, including in 1584 when Toyotomi Hideyoshi and his 120,000 retainers used it to stage war against Tokugawa Ieyasu, whose forces were spread over Komaki Mountain. Owned by the same family from 1618 to 2004 (it's now under management of a foundation), it displays a few samurai outfits and offers a nice, expansive view over the river that's especially worth a look if you intend to join the nearby cormorant fishing. The castle is so diminutive you can see everything in 15 minutes.