Refraction Preview is the second level you visit while playing Over Again by PAHC the intended way. It’s noteworthy for being the only true impossible level in the Arg hunt (PAHC himself admitted to me it’s impossible)

You play through some old gameplay before the level starts noclipping and gives you the hints of looking for secret ways in Sepia by PAHC

Also mentions the lore of the secret rivalry between PAHC and cerufiffy as well as Gyre by Optical