Games like Underponder
Games like Underponder include Little Nightmares, Viewfinder, Little Nightmares II, Portal 2, and Superliminal. We matched them by the tags players give Underponder on Steam (Adventure, First-Person, Atmospheric, Psychedelic, and Puzzle Platformer): closest matches first, and among equally close ones the better-known games.

Little Nightmares
Shared: Adventure · Atmospheric · Puzzle Platformer

Viewfinder
Shared: First-Person · Puzzle Platformer · Puzzle

Little Nightmares II
Shared: Adventure · Atmospheric · Puzzle

Portal 2
Shared: First-Person · Singleplayer · Puzzle

Superliminal
Shared: First-Person · Puzzle · Singleplayer

LIMBO
Shared: Puzzle Platformer · Atmospheric · Puzzle

Poppy Playtime
Shared: First-Person · Singleplayer · Puzzle

INSIDE
Shared: Atmospheric · Puzzle Platformer · Dark

Portal
Shared: First-Person · Puzzle Platformer · Puzzle

The Room
Shared: Atmospheric · Adventure · Puzzle

Antichamber
Shared: First-Person · Puzzle · Adventure

Layers of Fear (2016)
Shared: Atmospheric · First-Person · Adventure

Firewatch
Shared: Adventure · Atmospheric · First-Person

Outlast
Shared: First-Person · Atmospheric · Adventure

Seen
Shared: Adventure · Atmospheric · Singleplayer

What Remains of Edith Finch
Shared: Atmospheric · First-Person · Adventure

Hellblade: Senua's Sacrifice
Shared: Atmospheric · Adventure · Psychological

DARQ: Complete Edition
Shared: Adventure · Atmospheric · Puzzle

A Story About My Uncle
Shared: Adventure · First-Person · Atmospheric

The Talos Principle
Shared: First-Person · Puzzle · Atmospheric

Stray
Shared: Adventure · Atmospheric · Singleplayer

FAR: Lone Sails
Shared: Adventure · Atmospheric · Singleplayer

The Last Campfire
Shared: Adventure · Puzzle · Atmospheric

Bendy and the Ink Machine
Shared: First-Person · Puzzle · Singleplayer