Which famous door can not be opened from the outside?

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

Many German and British 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 famous by the luminance of Christ.

The absence of any outside knob on the door indicates that one must open one’s heart to Christ from within.