Dark Crypt Demo

This achievement was only available in the versions of the game that existed during the first week of October 2021. However, you can simply depot back to a version of the game that still has the unlock enabled.

-app 1749490 -depot 1749491 -manifest 2990368177563886055

You need to finish the game in order to get the achievement (you can skip credits). To get it quickly, you can just skip to level 15 and follow this solution:

← → 7↑ 4→ (lever) 3↓ 5→ 2↓ ← ↓ → (lever) ↓ space 4← space 5→ (lever)
2↑ 2↓ ← → 2↑ 4→ 2↑ 4← space 2→ space 2↑ 2→ ↑
(thanks Klumb3r)