I’m guessing you’re talking about the White Palace. It’s required for the “true” ending but you can reach the credits without it. It’s worth watching mossbag’s lore videos on YouTube whether you beat the game or not.

Zachtronics games are hard. Every once in a while I try going back to beat Spacechem but I’ll just hit a wall, noodle with it for a few days and just sort of run out of motivation.

STOP SMOKIN DA BOOF