By 'immersive anime', I'm referring to the shows that were able to seemingly blur the line between fantasy and reality, absorb you and make you feel as if you've been transported into their world or are experiencing the story through the MC's eyes, either through world-building, dialogue, atmosphere, etc.

I'll start off by throwing out a couple of my favorites:

Angel's Egg, a 1-hour, mostly dialogue-free OVA with deliberate pacing; a haunting soundtrack; and surreal, artistic visuals that worked together to suck me into its demented world

Otona Joshi no Anime Time: very underappreciated josei 4-episode OVA, very personal stories where it was almost as if I was experiencing the same emotions and struggles the women in the stories were.

So r/anime, what are some of the most immersive anime you've ever watched, and what aspects of the shows pulled you in?