Video games have the ability to immerse players in a way like no other art form, leaving them riddled with anxiety and soaked with sweat after finally making their way through an intense and demanding level.
It is a unique type of involvement reserved for the medium, and often these high-stress missions end up the most iconic and memorable parts of their respective games.
These 10 levels may not have been the most strictly difficult of each game, but their thick mood and challenging gameplay combined to ensure they induced dread and hopelessness like nothing else.
As a result, most every player took at least a couple of attempts to make it through these levels in one piece, overwhelmed by the game's aggressive attempts to oppress their spirit and prevent them from progressing any further.
As such, you shouldn't ever feel bad for struggling to make it through these levels, though when you finally did succeed it only made the triumph that much sweeter.
And yet, nobody could blame you for putting the game down for a day or two after getting through these sections...
10. We Don't Go To Ravenholm - Half-Life 2
Half-Life 2 may be one of the greatest FPS games of all time, but it gets its most gut-wrenching level out of the way relatively early, when Gordon Freeman takes a trip through the zombie-infested ghost town of Ravenholm.
We Don't Go to Ravenholm is a half-hour exercise in perfectly calibrated tension, steering the game quite unexpectedly into horror territory as players traipse through the blood-soaked, poorly-lit, resource-scarce, insanely creepy town.
The sheer atmosphere of Ravenholm throws most players for a loop, making it incredibly easy for a pack of Headcrab zombies to catch them off-guard.
But what offers the most potent threat of all in the town is the new Poison Headcrab, which with one quick dive towards your face will temporarily drop your HP to 1, making you an easy mark for any creatures in the vicinity.
Ravenholm marked a bold artistic departure for the series, yet was ultimately effective enough to permanently stamp itself on the brains of anyone who dared play it.