Depends on the game/level.
Stuff like mazes can even be done with a simple .txt file.
Years ago, I created a 3D level editor in Blitz3D to play around with a dungeon crawler idea.
The walls, columns, ceilings, floors and doors are just cubes with some textures I found online to test, so nothing fancy there...
Here's a video of some pre-alpha stuff. I didn't pursue it any further because Blitz3D was already too old at that point.
This is not fullscreen as Blitz3D doesn't run in Exclusive FS mode on Win10 w/o issues, or at all.
PSY