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.
Publicly published test chambers can be found at https://steamcommunity.com/id/irny/myworkshopfiles/?appid=620
Here’s a medium-difficulty puzzle that combines a lot of elements. Split over three main spaces, all solutions connect back to features in the initial room; lighting helps to provide guidance on possible solutions. This playthrough is recorded with commentary explaining some of my design choices.
Here’s an example of a simple puzzle where I wanted to create something that would fit into the confined default space provided by the level editor: