The allure of Castle Rock mostly comes from Jack's own perception of its "cool factor." He is, after all, a young boy, easily enamored by the glamour of having a fort. Castle Rock, in Jack's eyes, seems like the perfect place for several reasons. He sees Castle Rock as being easily defended, with its large boulders:
"Shove a palm trunk under that and if an enemy came-- look! [...] One heave, [...] and whee--!" (106).
He also maintains that the area is very livable, despite Ralph's opinion that "this is a rotten place" (106). Jack points out a fresh water drip from the rocks, where he could "keep a coconut shell there, filling all the time" (106).
Jack's attraction to Castle Rock reveals several important aspects about his character. He likes the idea of defense and attack, viewing the area from the perspective of violence and outsmarting the enemy. Jack's response to Castle Rock reveals him to be a tactical thinker, one concerned with maneuvers and strategy. Ralph sees the fort as a dismal, dreary place, but Jack is more of the visionary, seeing the fort as a possibility, a future place where he could be chief and reign supreme.
because it was a good idea for him to gain protection from enemies and as well ithere was running water.