Cthulhu: The Cosmic Abyss

Complete walkthrough, achievements, endings, and guides for Cthulhu: The Cosmic Abyss. Walkthroughs for the demo (Chapters 1–2), achievement routes, endings overview, and sanity tips — all static, no database.

View on Steam Start walkthrough

Chapter 1

Awakening — May's house, clues, basement puzzle.

Achievements

Thanks Key, Elementary, demo milestones, and more.

Endings

Good, bad, secret, and true ending frameworks.

FAQ

How do I unlock Thanks Key?

Have KEY analyze 25 distinct clues. Chapters 1 and 2 of the demo contain more than half of them if you scan thoroughly.

Where is the quartz alloy?

Near the occult book pages on the shelves in May's house. Scan it on the Mineral sonar frequency when KEY unlocks that step.

I missed a clue — can I go back?

Most demo areas allow free backtracking inside the chapter. If a door locks, reload an earlier save if available.

Hardest achievement in the demo?

Thanks Key or full frequency coverage — both reward slow, methodical scanning.

Does this wiki spoil the full game?

Chapters 3–7 are placeholders until release. Demo content is described in detail.