You found the fixed point.

Y f = f (Y f). A fixed point is what a function leaves unchanged — the value that survives its own transformation.

A quine is a fixed point of “run this”: a program whose output is its own source. In Python:

s = 's = %r\nprint(s %% s)'
print(s % s)

You looked beneath the page, decoded the door, and arrived. There is, of course, one more level down.