Colossal Cave

Throughout the game, you'll come across magic words written on the walls, which you must read to add to your repertoire (it appears in the inventory screen, to the right).

There are four "words", which can be found as follows:

XYZZY - Upon first entering the cave, you'll come across the Debris room, where a stream of water is flowing down and bringing some debris with it. Opposite to the water stream is a sign on the wall with this word written on it. Eyeball it to read it and add it to your repertoire.

PLUGH - After you defeat the snake, you'll be able to access three rooms - two chambers with treasures inside and a corridor that ends on a room with a sign that reads Y2. As you step inside, you'll hear the word PLUGH, and it'll be added to your repertoire.

FEE FIE FOE FOO - After fully growing the beanstalk, you'll be able to climb it and reach a new set of rooms with a locked door. On your way to the locked door, you'll be able to see the magic words written on the wall, before entering the door's corridor.

PLOVER (bird chirp) - The fourth magic word is more of a whistle or a bird chirp. After reaching the Orient room, you'll come across a narrow passage glowing green, which you can't cross with your inventory. Drop all of your items and cross the gap, which will land you in a room with some treasure near a bird to your right and a dark room to your left. Go right, grab the treasure, then turn around and step into the dark room. The narrator will warn you that you may fall down a pit if you go forward, so turn around and go towards the bird. If it doesn't chirp, turn around again and go into the pit, wait a second and come back out. To me, the bird chirped on the second time I stepped outside of the dark room. As soon as it does, the chirp should be added to your notes.

Once you unlock the fourth magic word, whichever it is, the achievement should pop.