Many techniques for caves : - Create a terrain and simply place the camera 'inside' it with a couple of point lights. - Substract a terrain from a cube - Create two terrains. Place one horizontally and reduce its vertical size. Place the other one vertically or upside-down, above the first one. With the correct lights, this will give the illusion of a cave.

Example of cave : - Start with a terrain with low altitude. Apply 'lunar crater' many times in the terrain editor. This is the purple terrain. - Take a large terrain and invert it with the terrain editor. Flip it over the first one. This one is the blue terrain. - Add a medium terrain to covert the junction between the first two. I eroded this one with 'canyon'. This is the green one. - Finish up with a water plane and a good atmosphere ('orbit' in the volumetric atmospheres or 'night' in the Others are good starting points).

Here is the result. I used the lanscape material 'chipped with paths' for the rocks, with the highlights tuned higher to give a 'wet' look. Have fun :)

Note: Here is a snapshot of the exact location of the wireframe object color tab. You can use this to give a different color to the wireframe model of the terrains.