Oswald Bastable and Others by Edith Nesbit

The children called him Sir Christopher Cockleshell. -- 'Sir,' in token of respect for his gray hairs and noble-looking face; Christopher, because he had once carried Mabel across the road on a very muddy day, when thunder showers and the parish water-carts had both been particularly busy; and Cockleshell, because of the house he lived in.

It was a most wonderful house -- like the gateway of an old castle. It had a big arch in the middle and a window over the arch, and there were windows, too, in the towers on each side of the arch. All along the top were in-and-out battlements. It had been covered with white plaster once, but flakes of this had fallen away and showed the pinky bricks underneath. But the oddest thing about the house was the trimming that ran all round the bottom story about the height of a tall man. This trimming was of oyster-shells, and cockle-shells, and mussel-shells, and whelk-shells, and scallop-shells, all stuck on the wall of the house in patterns. It was a very wonderful house indeed, and the children always tried to go past it on their way to everywhere.