This is a collection of levels, which use (usually) one gadget per map. They are generally hard to very hard maps, though you might find them easy, if you already know a trick or two. All of these will require you to think with portals, not just to use cubes and buttons. (Though that is - of course - an important part, too).
Please do not scream "these are impossible without glitches" or "you are trolling us". All of these levels are thouroughly tested and solvable. If you find them too hard, please do not downvote them. If you don't like them, tell me why. If you do like them, tell me why!
If you have questions, always use the spoiler-tags to not give away any hints.