For the first 23 achievements, you must go to Cheat Codes, the second voice on the main menu, click enter on A B A D and hit Enter. This will open you all levels, but the very last one will be unbeaten.

By the way, that's not "extra-game" cheating since it's already in the Steam official game, just like the various Final Fantasy in-game powerups. So, you need only the game, no other programs or such and if you want, you can manually travel through all the levels without problems. This command will "open" all the levels.



Hit Return to Menu, Level Select, Next World two times until you are on the Scalium menu. There, play the 8 level.
There aren't many videos or explanations about the game controls, here you'll need only few steps at normal speed. Keep in mind that if you close the game, you'll have to type the cheat code again.

Run right into the small corridor (WASD or normal direction keys), wait for the northern platform to get to the left and hit up.
This will bring the red thing UNDER the platform.



Run to the right, and click down at the end in order to drop the thing on the machine that will open the left part of the area.



Then, hit up fast or wait for the platform to come back again; you'll have to drop it again with the down key in the central niche in order to turn the machine green and remove the last barrier.



Run on the left again, you'll find that the wall has vanished. Hit up to be upside down on the ceiling, then hold shift and hit/hold the spacebar in order to long-jump over the two wheels. It's quite easy, maybe you'll have to try two or three times. Remember to hold both shift and the spacebar to complete the jump.



Then, press the E key to open the door and gain the "World 3, Level 8 Complete!" achievement.