The voice led him to a secret opening that no other person or creature could see, and he entered the mountain.

There is a secret opening in the wall of the landing, through which he could have easily gone.

And I may learn where the secret opening is!

None of the walls revealed a possible secret opening.

The secret opening is half a mile onwards upon the other side of the river.

There was again no sign of a secret opening, although he searched diligently for one.

No ships could get in or out without the secret openings being unlocked.

There is a secret opening in the stone floor; it leads to a vault below.

It followed that this room, like the meeting place, had a secret opening in the wall.

"You must make a secret opening in this wall."