This is the enclosure right next to Hon-maru and Higashi-no-maru.
”Tsuru-no-maru” literally means the enclosure of cranes.
Hoshun-in, the wife of the first feudal lord Maeda Toshiie, saw a white crane fly down to this enclosure, and named it ”Tsuru-no-maru”, saying the crane was a good omen showing that the Maeda Family would prosper for a long time.
The second lord, Toshinaga, built a rest house and maintained his watch over the government from here.
Later, they built a building to keep prisoners too.