I'm creating a game and making my models in Blender. I have a scene where players can walk inside a volcano. The problem is whenever they walk inside the volcano seems to disappear. This is the same with all of my objects. I'm not sure what the problem is.
You have to model both sides of an object, the inside and the outside, in order for it to be visible. Polygons viewed from the "wrong" side are invisible. (Technically you can use a shader with "cull off" to make polygons be double-sided, but both sides will have the same lighting, which is not usually what you want, so you might as well just go ahead and model both sides properly.)