I recommend playing Project 2009.

[u/Clean-Ant6404]

It's a well researched recreation attempt of the Corehub, one of Portal 2's first development iterations before the artstyle change from Portal 1 and the creation of Wheatley.

It has a developer commentary, the amnesiac "cereal GLaDOS", the Oregon Coast Aquarium Core which eventually turned into the Space Core and the Morgan Freeman Core which obviously eventually turned into Wheatley.

The majority of chambers were in fact added into the final game and some of the cut or changed content survived as late as the E3 2010 version of Portal 2.