Linked portal

Linked portals (development versions only) are a powerful feature which make it possible to connect two separate areas of a map via the floor/ceiling or one-sided linedefs, allowing the player to see, shoot, and even move seamlessly from one area into another. They are used similarly to two-way portals, apart from the fact that you can pass through them. They can be used to create 3D architecture and room-over-room effects, with very few limitations.

Line triggers

358 - Linked portal ceiling 359 - Linked portal floor 360 - Linked ceiling anchor 361 - Linked floor anchor 376 - Linked portal line (front) 377 - Linked portal line (back)

Tutorial

An in-depth visual tutorial on the creation of floor/ceiling linked portals can be found here. (Thanks, zarkyb!)