Games like The 18th Floor
Games like The 18th Floor include Murders on the Yangtze River, Cyber Manhunt, Sanfu, The Exit 8, and The Operator. We matched them by the tags players give The 18th Floor on Steam (Puzzle Platformer, Immersive Sim, Dungeon Crawler, Puzzle, and Underground): closest matches first, and among equally close ones the better-known games.

Murders on the Yangtze River
Shared: Puzzle · Detective · Puzzle Platformer

Cyber Manhunt
Shared: Puzzle · RPG · Detective

Sanfu
Shared: Puzzle · RPG · Puzzle Platformer

The Exit 8
Shared: Puzzle · Immersive Sim · Underground

The Operator
Shared: Detective · Puzzle · Immersive Sim

Unheard - Voices of Crime
Shared: Detective · Puzzle · RPG

THE 4 SINS
Shared: Puzzle · Immersive Sim · RPG

Supraworld
Shared: Puzzle · Immersive Sim · Puzzle Platformer

LIMBO
Shared: Puzzle Platformer · Puzzle · Indie

Shadows of Doubt
Shared: Immersive Sim · Detective · Puzzle

DEEMO -Reborn-
Shared: Puzzle · Puzzle Platformer · Immersive Sim

Return of the Obra Dinn
Shared: Puzzle · Detective · Mystery

Sherlock Holmes: The Devil's Daughter
Shared: Detective · Puzzle · Adventure

Monument Valley 2
Shared: Puzzle · Strategy · Puzzle Platformer

Mandate Of Heaven
Shared: RPG · Puzzle · Immersive Sim

Firework
Shared: Puzzle · Indie · Mystery

Scarlet Idol
Shared: Puzzle · Dungeon Crawler · Puzzle Platformer

Moncage
Shared: Puzzle · Casual · Indie

Paper Bride
Shared: Puzzle · Detective · Puzzle Platformer

Portal
Shared: Puzzle Platformer · Puzzle · First-Person

Monument Valley
Shared: Puzzle · Strategy · Puzzle Platformer

Human Fall Flat
Shared: Puzzle · Puzzle Platformer · Adventure

COCOON
Shared: Puzzle · Puzzle Platformer · Adventure

Little Nightmares
Shared: Puzzle Platformer · Puzzle · Adventure