Just found this super useful website for level designers -- https://noclip.website/ The website lets you god view through some of the most iconic games. When viewing levels this way, you can really see all the gates and valves and textures and keys and gates working together to create an engaging player experience. I've made a little compilation of all my favourite level designs that I could pull from my first 5 minutes of using this... there's plenty of advanced features as well, like switching off textures, vertex colouring and post process effects, which makes it really interesting to see the level without all the tiny little hacks that game designers used to create more immersion, like fog, or high quality textures on low poly meshes. This is gold.