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If you’re a good-practice mapper, you’d make the curved surfaces and those support beams a brush entity, making them pretty much ignored during all but the lighting stage of compiling.
[This means the interior of the map ‘leaks’ into the void](https://developer.valvesoftware.com/w/images/f/fe/Hammer_leaks5.jpg) unless blocked by another world brush. All Source-engine and Goldsrc maps have to be internally sealed.There are more complex reasons for leaks, but that’s the basic idea; an entity touches the cold, dark, soulless void leading to it devouring your map’s functionality.