The image below attempts to explain what I am on about.
I create an obect with enclosed holes. For example, a raised walkway around a square. Or a wall with a big window in the middle. In theory an object moving in the square or through the window should not have any interaction with the walkway or wall. However on importing into an mmo the empty spaces turn out to be not holes at all, but invisible surfaces. So what looks like a hole or emptiness acts like a solid, and other objects attempting to move through the “empty” space collide and stop.
Also, using any modelling program (I am new to all this, regardless of software) I cannot see anything (polygons, whatever) in the emptiness.
So … how can I make actual holes using sketchup? Remove things or enclose spaces that really have nothing actually there?