Here's how to beat Exit 8:
I know the game kinda just throws you into it without much instruction, but at the beginning of the game, near the big yellow signs on the wall that say exit 0, 1, 2, etc... you'll see a sign next to it explaining the rules.
These are the rules:
1) Always check for anomalies - Each room has the chance to have an 'anomaly.' These aren't all super easy to spot right away, so take a few trial runs and carefully study the layout of the tunnel. Anomalies will be easier to spot the more times you go through the tunnel. An anomaly can range from something simple like a door closing, to something like a river of blood flooding the hallway.
2) If you see an anomaly, turn back immediately - If you spot an anomaly, turn around and go back to where you came from. The hallway will essentially 'turn around' and progress you in the game if you successfully avoid an anomaly (you'll see more of what I mean as you play).
3) If you don't notice any anomalies, continue on - If you don't notice any anomalies, continue going down the hallway. I would advise you to check carefully though, especially when you don't notice an anomaly.
4) To leave, reach exit 8 - As mentioned in the beginning, there is a big sign on the wall that says exit __. If you successfully notice an anomaly, or continue through the hall when no anomaly is present, the number on the exit sign will go up (going back down to 0 when you fail either one). The number goes to 8 (hence the name exit 8), but be careful, just because you reached exit 8 doesn't mean you're done. Read this next part only once you come to exit 8:
*** Spoiler - click to reveal *** When at the exit 8 hallway, there is still a chance to be an anomaly. If you see an anomaly, follow the rules and turn back around. Don't be discouraged when you see the exit 8 sign again, as you're still close to the end. To truly finish the game, you must wait until there are no anomalies in the exit 8 hallway. From there you can continue on, to find a staircase. Follow it up and you've finished the game and got the achievement.
For me, the achievement didn't pop the first time I went up the stairs. I had to play the game over again when it respawned me after the credits the first time to actually get the achievement. I'm not sure if this is intentional or not, but by the time you beat it the first time you'll be pretty proficient, and should be able to do the next 8 with relative ease.