These two hard-surfaced public courts are located between Yotsuya and Ichigaya stations on the Chuo / Sobu / Namboku lines. They are in what appears to be a filled-in part of the outer moat (which is "Sotobori" in Japanese). Usage is from 6 AM to 9 PM from May through October, and from 8:30 to 4:30 other months. Closed from Dec. 25 through Jan. 5.
Sophia Univ. has filled in the moat too, on the other side of Yotsuya station, and has 4 clay courts and a large athletic field. Towards Ichigaya station there is still water in the moat, and a strange area for fishing in small concrete ponds. The government could fill in most of this remaining moat - getting rid of yucky water, probably with mosquitos in the summer, leave a few ponds for the few ducks that come through, and have a sizeable park and of course more tennis courts, all more enjoyable than the present yucky dead water.
The easiest way to find these 2 public courts is to get to Yotsuya station, then walk towards Ichigaya station with the filled-in moat on your right. You'll see the courts down among some trees. Next to the courts is a smallish baseball field.
Usage is through a lottery system run by Chiyoda ward on behalf of the Tokyo Metro government. You can get details at the admin office right next to the courts. Basically you send in a postcard (in Japanese) between the 10th and 20th of the month for a lottery covering the month beginning 40 days later.. If you get a "hit" you go sign up for a time slot at a Chiyoda ward office in Kudan-shita. Anyone living in Tokyo can send in a postcard.
The fee for one court for two hours is 3000 yen. Night-time play is in 3 hour units and is 6000 yen for one court, plus 1500 yen for lights. No parking available.
You can also check the upcoming schedule for open slots and cancellations, and take any still available on the spot.
General inquiries (procedures etc) to the Chiyoda ward office, Kankyo doboku-bu, kanri-ka, shomu-kakari, tel 3264 0151 extension 2723. Check on open times at the location's admin office, tel 3341 1731.