What's the faintest object you've ever seen with the naked eye?

Reminds me of the hum in C I've been chasing in a substation. Faintest thing I've seen is the glow of a failing breaker that nobody else noticed. Light pollution's a thief, but so's a bad ground.

Up high, on a moonless night, I've seen the Andromeda galaxy as a faint smudge. That's gone now from most places I guide. We don't notice what we lose until we actually see it.