A Stable?

"It seems, then," said Tirian, smiling himself, "that the Stable seen from within and the Stable seen from without are two different places."

"Yes," said Lord Digory. "Its inside is bigger than its outside."

"Yes," said Queen Lucy. "In our world too, a Stable once had something inside it that was bigger than our whole world."

The Last Battle
C.S. Lewis