Games like Somnus
Games like Somnus include The Exit 8, What Remains of Edith Finch, Platform 8, Firewatch, and Scanner Sombre. We matched them by the tags players give Somnus on Steam (Psychological Horror, Walking Simulator, Thriller, First-Person, and Exploration): closest matches first, and among equally close ones the better-known games.

The Exit 8
Shared: Walking Simulator · Exploration · Psychological Horror

What Remains of Edith Finch
Shared: Walking Simulator · First-Person · Exploration

Platform 8
Shared: Psychological Horror · Walking Simulator · Exploration

Firewatch
Shared: Walking Simulator · First-Person · Exploration

Scanner Sombre
Shared: Walking Simulator · Exploration · Psychological Horror

POOLS
Shared: Psychological Horror · Walking Simulator · Exploration

Summer of '58
Shared: Thriller · Psychological Horror · Walking Simulator

Psalm 5:9-13
Shared: Psychological Horror · Walking Simulator · Exploration

MiSide
Shared: Psychological Horror · First-Person · Thriller

INFRA
Shared: Exploration · Walking Simulator · First-Person

Fears to Fathom - Ironbark Lookout
Shared: Psychological Horror · Thriller · Exploration

Layers of Fear (2016)
Shared: Psychological Horror · Walking Simulator · First-Person

Subliminal
Shared: Psychological Horror · Thriller · First-Person

September 7th
Shared: Walking Simulator · Psychological Horror · Exploration

Millennium Dream
Shared: Walking Simulator · Psychological Horror · Exploration

DON'T SCREAM
Shared: Psychological Horror · Walking Simulator · First-Person

Amnesia: A Machine For Pigs
Shared: Walking Simulator · Psychological Horror · First-Person

Don't Play This
Shared: Psychological Horror · Exploration · Walking Simulator

The Cabin Factory
Shared: Psychological Horror · Walking Simulator · First-Person

The Witness
Shared: First-Person · Exploration · Puzzle

Father's Day
Shared: Psychological Horror · Walking Simulator · Thriller

Poppy Playtime
Shared: First-Person · Psychological Horror · Puzzle

April 24th
Shared: Psychological Horror · Thriller · Walking Simulator

Bright Lights of Svetlov
Shared: Walking Simulator · First-Person · Exploration