Start a new game on easy and equip yourself with the Amnesia perk. Now, you will need to spend 50 turns in order to activate the perk.
What I did, was I walked back and forth on the 99th level of the apartment complex until my Hunger was at 0. I used the food and bandages found on said floor to sustain me and I went to the 98th level, fought the monster, and used the supplies on that floor. I kept walking until I used up all 50 turns. Then, you must click on the perk (upper left hand corner, beside your health and food bars). It will automatically transport you to level 50. Once you've activated the perk, achievement unlocked.
Note: You only unlock perks after you have beat the game at least once!