Developer and Tech Artist ごんびぃ has recently impressed thousands of people over on Twitter by showcasing an absolutely jaw-dropping shader that opens the window to different worlds and, in the words of the author, "can't convey how amazing it is".
According to the author, the shader was set up in Unity via interior mapping and Skybox masking. To achieve the stunning result seen in the demo above, the creator added a masking feature to the Cubemap Shader, so that when you peek through the 'window', you can see a different Skybox, meaning that there are multiple Skyboxes in the scene.