They just flew softly on, till suddenly Dudu veered to one side and stopped them in front of a low carved door with a step before it just large enough for them to stand on.

They had not noticed this door before--the hall was so very large and the door in comparison so small, and the step before it had looked just like a little jutting-out ledge in the carving, till they were close to it.
"Don't turn round," said Dudu, "for fear it should make you giddy.

Push the door and go in at once." The children did so.

The door yielded, and then immediately--they were such well-behaved doors in the tapestry palace--closed behind them.

And what the children now saw was a small winding stair, the lowest steps of which were close to their feet.
"Here," said Dudu, "I will leave you.