Kōka (甲賀市) is a city in Shiga prefecture, Japan.
Kōka is best known as the home of the Koga ninja clan, rivals of the nearby Iga ninja. Unlike the Iga ninja, whose power was well-known, the Koga clan are said to have used stealth and deception to mask their size and power, creating fake rivals for themselves. In 1581, the two clans joined forces against Oda Nobunaga, but were defeated by Nobunaga's overwhelming forces, and the surviving members of the Koga ninja went into retreat.
The smaller cities of Shigaraki, Tsuchiyama, and Kōnan merged into Kōka in 2004.
Kōka is on the JR Kusatsu Line.
Free shuttle buses are available from JR Koka station to the Ninja Village, but prior booking is necessary.
- Ninjyutsu Yashiki (Ryuhoji Konan-cho, Koka-shi; 9:00am-4:30pm, closed 12/27-1/1. Admission ¥500 adults, ¥300 children ages 6-12.) Ninjas had to sleep somewhere; this normal-looking old Japanese house has all of the trapdoors, fake walls and other gadgetry that a ninja would need to feel right at home. Take the Kusatsu Line to JR Konan station. It's about 30 minutes away by foot.
- Ninja Village (394 Oki Koka-cho, Koka-shi; 9:00am-5:00pm, closed Mondays and 12/27-1/1. Admission ¥1000 adults, ¥800 children ages 13-18, ¥700 ages 6-12, ¥500 ages 3-6.) As the saying goes, it takes a village to raise a ninja, and this is that village. Facilities include a Ninjustsu museum, another ninja house, and a "shuriken school". Ninja uniforms are available for trying on and trying out on an obstacle course with walls and ropes. Kids receive a scroll certificate for completing the day's ninja lessons.
- Minakuchi Castle  was built in 1634 as a way-station for Tokugawa Iemitsu in his travels between Tokyo and Kyoto. The current reconstruction dates from 1991. It's on the Omi Tetsudo Line, a ten minute walk from Minakuchi Jonana station.
Iga is the other ninja hot-spot in Japan, and isn't far away.