In spite of the fact that this well was located at higher elevation than any other wells in the premises of Naegi Castle, the well never dried up even in dry weather, they say. The name "Sen-goku Well" ("Sen" means a thousand) came from a legend that the well could serve for a thousand people. Honmaruguchi-mon Gate, located on the west side of Sen-goku Well, separated Hon-maru (the main enclosure of a castle) and Ni-no-maru (outer citadel). The gate had a nickname "Keyaki (zelkova) Gate" since it was built of zelkova. On the north side of Sen-goku Well was a row of Kake-zukuri (overhang method of construction) storehouses named Shibugami-gura, Yamagata-gura, and Kōrigata-gura.