How do you get into the door in ruin valley?

How do you get into the door in ruin valley?

How do you ge into the door in ruin valley? Also, where is the dotted hole and how do you get in? I see it on the town map but I have looke all over ruin valley and it is not there! For my other question, the one about cerulean cave,I already have 110 types of Pokemon from the Kanto and 16 types for the national (not counting the kanto and national together)! Oh, I got both the hitmontop and hitmonlee!!