Collision Detection in 3D

I've been searching the web a little for this topic, but haven't found exactly what I'm looking for... I'm looking for some kind of algorithm for Collision Detection in 3D space using, for example, meshes with a lot of vertices (such as terrains)..

Right now, I'm not sure where to begin, so all help is very, very welcome :P...

The best thing to do is to search for Bounding Boxes. These are a good way of detecting if you've hit anything.