Creaks

Creaks begins in the bedroom of the unnamed player character, who is seen sitting at his desk when the light flickers and dies, and the wallpaper peels away to reveal a secret tunnel behind his wall. The protagonist ventures through the newly discovered tunnel and, after climbing down a ladder, finds himself in a massive mansion-like structure contained within an enormous cavern. He encounters aggressive monsters that become harmless inanimate objects when seen under the light. He also discovers that there is a giant feline monster slowly destroying the mansion by climbing on it.
While exploring the underground world, the protagonist also meets several friendly bird-like people; an elderly bird person searching for a codex in order to defeat the giant monster, a younger bird person who tries to fight it with weapons and traps, a scientist bird person who attempts to tame it, and a small mechanic with a pipe for a head who repairs the destruction caused.
The protagonist eventually reaches the bottom of the mansion, where he finds the scientist and the mechanic fighting the giant monster. It swallows the mechanic before retreating, and the scientist, saddened, leads the protagonist to her workshop, where it is revealed that she originally built the giant creature to power the mansion. The elder then arrives with the codex and reveals plans about a crystal, which the scientist builds a container lantern for. She then takes the protagonist further down into the sewers in search of it. He finds the crystal in a cavern and puts it into the lantern, creating a light that can defeat the giant monster.
They begin climbing back up to the top of the mansion, regroup with the other two bird folk, and prepare to fight the monster. The protagonist jumps into its mouth, encountering the mechanic still alive - the monster is made out of household objects. The protagonist releases the crystal, destroying the monster and rescuing the mechanic in the process. With the monster defeated, the protagonist says goodbye to the bird folk and climbs back up to his bedroom, closes the entrance to the underground world behind his wallpaper, and opens his window to find that it is now day time.