Karuizawa is a little over an hour from Tokyo Station by shinkansen, so a rental car is optional. That makes it easy to append to a Haneda or Narita itinerary, and many visitors combine it with time in Tokyo.
What defines Karuizawa is course density. Karuizawa 72 runs South, East, West and North courses, so you can fill several days by changing course rather than hotel, and a nine-hole option fits an arrival afternoon.
The altitude keeps midsummer cool, which is why July and August are busiest. In winter some courses close, and opening and closing dates shift year to year, so confirm operating periods before booking.
Comparing a Japanese tee time on the headline green fee alone tends to produce a different number at the counter. Confirm whether cart, caddie or self play, lunch, locker and the local golf tax are included, then check rental clubs or shoes, minimum player counts, two-player supplements, payment method and whether overseas visitors can book. Clubs may also specify check-in times, dress codes and bathing etiquette, so submit player names accurately.
Three nights in Karuizawa with two consecutive rounds at the 72 courses and one day toward Saku or Tateshina — or the outlet mall — keeps transfers lightest. With two nights, staying inside Karuizawa and changing course is safer.