Marathon 2 by Bungie also had weird non-euclidean maps with overlapping sections in the late 90s I think.
I miss the customizability of that game. Early bungie works were up there with early blizzard or early valve. They sold a tool for fun instead of casting a bait for profit.
I recall that some of the developer commentary for either Portal or Portal 2 mentioned that they began level-development by using a special version of the namesake non-euclidean Portals to connect different chambers and hallways that were being developed in parallel. [Per distinct loading-screen level.] Then, later in development, they ran a tool to stitch together all that geometry in a more-normal way, and they only had one case of impossible-overlap, which continued to use the non-euclidean link.
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Edit: Found it:
> [...] When we started the project making any big structural change in a level or the order of levels would lead to hours or even days of busy work trying to reconnect things and make sure they lined up again. If we ever wanted to ship something the size of Portal with the finely tuned balance we desired then we needed a way to be able to make big changes to the layout of the game without paying the cost of making everything line up again. We needed a way to bend space. We needed to think with portals. Using portals to connect different areas in the world we could make any type of impossible space work out. You could look through a hallway into the next room but the hallway might be on the other side of the map and the room you are looking into might be in a completely different orientation. We could seamlessly insert an elevator, a huge expansive vista, a room that was bigger on the inside than the outside, or even create an infinite fall by connecting a shaft back into itself. Soon every connection between any space was a portal. We would even switch them on the fly. Even a simple door worked like the cartoons - just a facade painted on a wall that seamlessly opened somewhere else entirely. Once the game settled down we were able to finalize our path and remove all of the world portals. There's only one impossible space left in the whole game - see if you can figure out where it is.
I miss the customizability of that game. Early bungie works were up there with early blizzard or early valve. They sold a tool for fun instead of casting a bait for profit.