The ivy is called "a loose and swinging curtain".

One of the nice little gusts of wind rushed down the walk, and it was a stronger one than the rest. It was strong enough to wave the branches of the trees, and it was more than strong enough to sway the trailing sprays of untrimmed ivy hanging from the wall. Mary had stepped close to the robin, and suddenly the gust of wind swung aside some loose ivy trails, and more suddenly still she jumped toward it and caught it in her hand. This she did because she had seen something under it—a round knob which had been covered by the leaves hanging over it. It was the knob of a door.

She put her hands under the leaves and began to pull and push them aside. Thick as the ivy hung, it nearly all was a loose and swinging curtain, though some had crept over wood and iron. Mary’s heart began to thump and her hands to shake a little in her delight and excitement. The robin kept singing and twittering away and tilting his head on one side, as if he were as excited as she was. What was this under her hands which was square and made of iron and which her fingers found a hole in?

It was the lock of the door which had been closed ten years and she put her hand in her pocket, drew out the key and found it fitted the keyhole. She put the key in and turned it. It took two hands to do it, but it did turn.