How do I show the inside of a cave?

I have a model of a cave (.dxf) and when I import it into Unity I can’t see it from the inside. I will need to walk around in it, and use the Physics features.

Add a light source first (like GBStudios said). Apply a double-sided material to it, if you can see the cave from the inside, then you need to flip the normals on your 3d modelling program.

It Sounds like the problum You are haveing is with your normals, flip the normals, or rectangulate to the inside, in a modeling program and it should be good to go. Most modeling programs rectangulate by default to the outside. Normals only show oneside, the other side is completely see through. Sometimes you may want to select the normals on the inside and flip them in so the normals on the outside still show out.