Making an invisible floor

Invisible floors is an effect that allows a level designer to put invisible solid sectors on a pit in which the player can walk, simulating flying or walking on mid-air. Designer Leo Lim first demonstrated the technique in NEWTECHN.WAD and later incorporated it into the playable map Doomsday of UAC. It was later used by the Casali brothers for the official map MAP02: Well of Souls (The Plutonia Experiment).

Implementation
There are several methods to obtain this effect. This is just one way of accomplishing this. Steps:
 * 1) Within an existing sector, create another sector, and then another within that one.
 * 2) Give the innermost sector the desired invisible floor height.
 * 3) Note the sector number of the innermost sector.
 * 4) Edit the innermost sector's surrounding lines so that the sector references on both sides are to the innermost sector.

Example

 * [[Media:SKYWALK.WAD | Example of this trick]] (file info).