Map

Sixth floor corridor, entrance on the left.

Accessible via the Leaky Cauldron

Go to the clock tower, go all the way down, through the clock tower courtyard, across the bridge and down the path.

Enter Diagon, walk forward turn right at Gringotts and turn right after Weasley Wizard Wheezes.

Through the painting left of the First floor corridor door on the Grand Staircase.

Go all the way down the First floor corridor.

Go north from the Training Grounds, through the Quidditch Hall of Fame and follow the path.

From the library's main entrance, turn around, walk outside, go forward and then left, and look for the stone ruins.