In Undying, on the first quest.
In the catacombs there are several levels with infinitely spawning skeletons. Skeletons in that game(in the beginning, before you get god mode spells and weapons) are.....the most horrifying things.
They shreak and yell, they come back to life after you kill them, the only way to to kill them completely drains your entire mana pool, which takes at least 50ish seconds to refill, and they throw spears with FUCKING UNERRING ACCURACY in addition to doing crazy melee damage. the only way to dodge the spears is to hold still, and then move exactly when the (very fast) projectile launches. They track your movement perfectly, and WILL hit you unless you change direction the second the projectile launches.
(you can also use other skeletons to block the spears, and then they'll fight each other, but there are so many that it doesn't help you much. it is hilarious though.)
And did I mention their numbers are constantly being reinforced? You have to run like a madman through the maze filled with unkillable monsters, ducking and dodging, madly searching for the exit, hoping you don't run into a dead end. then all the candles go out, and it's pitch black.
I hate the skeleton levels. They always kill me and then eat my still beating heart. literally.