Wiktionary
not a pretty sight
n. 1 (context euphemistic sometimes humorous English) Something visually unappealing, ranging from mildly unattractive to utterly disgusting in appearance. 2 (context idiomatic by extension English) Something disappointing, disquieting, disreputable, or otherwise unworthy of admiration.
Usage examples of "not a pretty sight".
Just be sure to step into the shadows if you do, as I imagine its not a pretty sight.
His naked body showed no signs of injury except for his wrists, which were not a pretty sight.
After the trolls had all been driven away, the castle yard was not a pretty sight to see.
The body was not a pretty sight, even by Klingon standards, but Stone did not seem the least bit phased by it.