Bridges

Fake 3D bridge, can only be walked over, solid floor texture

Fake 3D bridge, can be walked over/under, using midtextures

They're called 'self-referencing sectors'. Here's a tutorial on how to make one.

1 hour ago, NinjaDelphox said:

I cannot get the self referencing sector to work.

Assuming you have an editor in the DoomBuilder family, look at a random 2-sided linedef. The front (1st) side references a sector index, namely the sector that is in front of the linedef. The back (2nd) side references a different sector, namely the sector that is behind the linedef. This field can be edited.

If you create a sector A within a sector B and have the linedefs point inwards towards sector A (toggle 'f' in doombuilder to change orientation), you'll notice all the boundary linedefs point their front side to sector A and their back to sector B.

A self-referencing sector does not have any of its boundary linedefs point to any other sector than itself. In above example, that would mean that all the linedefs bordering sector A only point to A.  To do that, you need to replace the reference to sector B on the back side of those linedefs to sector A.

Perhaps I am still doing something wrong, because I cannot get the self referencing sector to work. I guess I am just dumb lol.

Yeah I know about changing the sector index that way, it's just that when I did it the sector seemed to bleed into others and acted all weird in game, but after messing around with it a bit more I think it is finally working, Thank you so much!