Ok this problem will not stop plaguing me. What can I use to simulate movement up/down a hill? I tried several things but I can''t seem to get it right. My current idea is to use the movement vector without the terrain (vVector) and take the dot product of that and the plane normal (to get a directional derivative). The only problem is that it doesn''t work. Sometimes I get sucked through the terrain for no apparent reason. Does someone want to help me out with my theory? I have limited knowledge of physics/math unfortunately . www.geocities.com/vsage3/projects.html is where the source code is if that helps you. The function in question is the MoveCamera function in Camera.cpp.