I’ve enjoyed revisiting Portal 2 and its popular level designer. I often sketch out rough plans for levels on paper and then iterate in-game. Below are two examples, each created to a different brief.
Publicly published test chambers can be found at https://steamcommunity.com/id/irny/myworkshopfiles/?appid=620
Level 1: You Can Take it With You
Was that portal orange or blue?
Here’s a medium-difficulty puzzle that utilises a variety of approaches. Split over three main spaces, all solutions connect back to features in the initial room, making this chamber at least partially a test of memory; lighting helps to provide guidance on possible solutions. This play-through is recorded with commentary explaining some of my design choices.
Level 2: Basement Flooding
Here’s an example of a simple puzzle where I worked to create something that would fit into the confined default space provided by the level editor: