1.   A visitor treks to the pumps from the darkened viewing room of the aquarium by opening an unmarked door.

2.   I try an unmarked door and it opens to reveal ... yes, stationery again.

3.   The Skunk Works operated as an independent community within Lockheed, its secret activities conducted behind unmarked doors.

4.   She led us to an unmarked oak door which opened into a short corridor, obviously a modern extension to the farmhouse.

5.   I try an unmarked door and it opens to reveal... yes, stationery again.

6.   He scurried to the side of the building and knocked on an unmarked door.

7.   He left the room, escorted by Levy, through an unmarked door.

8.   In a nondescript building, up a flight of stairs and behind unmarked doors, a dozen ultra-Orthodox men sat hunched over desks, furiously coloring away.

9.   The lactation rooms, behind an unmarked door, restrict access by requiring users to punch in security codes, which are changed twice a year.

10.   Recently, he said the program was previewed by unidentified people behind an unmarked door before it went on air.