eye doing the opposite is easier, but i dont see how much can it differs from the standard cave entrance tiles with faded to black stone texture, after all down there is darkness!! the real thrill is looking up to the sky and seeing it change from day to night, while you're still in the cave network
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also, using a skybox "window" allows to cut the texture need to just 4 (day/daynight/night/nightday) for each single skybox (that can be a panorama, imagine desert one, forest one, city one, etc etc