how to make camera look through objects from only one side? I have modeled a rather small room, and when trying to get the right camera angles I can't fit the camera inside the room without getting too close, so I wan't the walls and ceiling only to be visible if the camera is placed inside the room. Understand?

Make it so the camera can look through the ceiling and walls from the outside, but they still appear in the cameras view when the camera is on the inside looking out?
Final result:

This is kinda same idea as @Duarte Farrajota Ramos but it is working in Cycles (viewport/camera).



Mesh:

Your mesh normals should point to the inside of the room as in the image below.



Materials:

You will need to assign different materials for floor and walls and ceiling.



Floor material. Could be anything you want.

Wall and ceiling material. Should look like this and in the place of red Diffuse you can and anything you want. Remember to check if Transparent shader color is pure white. Hex value #FFFFFF.