He knew its outside perfectly, and now his business was to get his notion of the inside right with the outside.
So he shut his eyes and made a picture of the outside of it in his mind.

Then he came in at the door of the picture, and yet kept the picture before him all the time--for you can do that kind of thing in your mind--and took every turn of the stair over again, always watching to remember, every time he turned his face, how the tower lay, and then when he came to himself at the top where he stood, he knew exactly where it was, and walked at once in the right direction.
On his way, however, he came to another stair, and up that he went, of course, watching still at every turn how the tower must lie.

At the top of this stair was yet another--they were the stairs up which the princess ran when first, without knowing it, she was on her way to find her great-great-grandmother.

At the top of the second stair he could go no farther, and must therefore set out again to find the tower, which, as it rose far above the rest of the house, must have the last of its stairs inside itself.
Having watched every turn to the very last, he still knew quite well in what direction he must go to find it, so he left the stair and went down a passage that led, if not exactly toward it, yet nearer it.

This passage was rather dark, for it was very long, with only one window at the end, and although there were doors on both sides of it, they were all shut.