[jalbertoni]

The original Doom engine does not have it, but a very popular port called Boom added many new things and one of them was a silent teleporter, as in, walk over a line and get teleported to the same position in a line of the same length somewhere else. It can be used to make many interesting effects. I used them in... I don't want to say every single one of my maps, but 90% for sure. The one caveat is that they don't render what's on the other side, so you have to recreate the geometry manually and monsters will suddenly disappear or appear.

Vertical, floor-to-ceiling portals are a bit more new. I think only the Eternity Engine and GZDoom support those. They also support portals that render the other side, monsters and everything.

Edit: Oh, I forgot that you can get portal-like behavior in the Vanilla engine by hacking the BSP tree used for rendering, see https://doomwiki.org/wiki/Linguortal and also here for a more visual demonstration: https://www.doomworld.com/vb/thread/74354

[hnlmorg]

Yeah but like the GP said, the other commenter was confusing Doom with Build. What they described wasn’t a feature in the original Doom engine however it was a common trick used in original titles on the Build engine.

If I recall correctly, the only way Doom (the game) achieved dissecting planes was to have stepping stones.

[smcl]

Wow I had no idea - every day's a school day! Thanks for sending those links over, the Doom engine continues to surprise me :D