Which famous door cannot be opened from the outside?

Here is a thought: Christ at Heart’s Door.

Many British and German religious prints from the nineteenth century depict Christ knocking at the door of a home, symbolizing Jesus Christ’s importance at both a friend and a guest. The most famous of these images are the versions of The Light of the World by William Holman Hunt, the first of which Hunt completed in 1853 and which hangs today in Keble College, Oxford. In 1947, Warner E. Sallman rendered a 21st century version called Christ at Heart’s Door, in which a barely concealed heart on the doorway made prominent by the luminance of Christ. The absence of any outside knob or latch on the door indicates that one must open one’s heart to Christ from within.

https://doorsinmotioninc.com/which-famous-door-can-not-be-opened-from-the-outside

Also, the "Door to Nowhere" at Winchester Mystery House, which opens directly to the outside from the second floor.

https://www.popsugar.com/smart-living/What-Winchester-Mystery-House-44167586

The big wooden doors in China that President Bush tried to escape from during his news conference.

http://news.bbc.co.uk/2/hi/asia-pacific/4454738.stm

The Doors of Perception? (But they are plural).

http://mescaline.com/huxley.htm

The door of Number 10 Downing Street cannot be opened from the outside. There is always someone inside to open it.

A police officer traditionally stands outside the black front door of Number 10 — a door which has no keyhole on the outside; it can only be opened from the inside. A second police officer is on permanent duty on the other side of the front door, so there is always someone there to open it for the Prime Minister.

https://en.wikipedia.org/wiki/10_Downing_Street

Just for good measure, I'd like to add Thorndike's Puzzle Box, which should be well-known to the psych buffs out there:

To study trial and error learning, Thorndike used a type of test pioneered years earlier by Watson: the puzzle box. Originally, Watson's puzzle box (shown in the illustration) required a monkey to reach through the cage to lift a latch. Thorndike substituted a foot-pedal so the research could be done with cats. If the animal stepped on the switch, the door of the cage opened. The object of the research was to study how quickly the cat learned to perform this response in order to get free. Today this would be called escape learning.

http://www.intropsych.com/ch08_animals/thorndikes_puzzle_box.html

https://en.wikipedia.org/wiki/Edward_Thorndike