Did you make a cave in a level with this method? Normally, there occure several difficulties until a new solution like this fits with the purposes of a level!

Walls with smearing textures at the walls comes to my mind when I think of terrains as caves!

http://www.puppenheim.org/
http://www.wuerfels-welt.de
Old Game Tutorial: http://www.puppenheim.org/MITutorial.zip
Free Game Editor: http://puppenheim.org/AlienalsWeihnachtsmann.zip
http://www.puppenheim.org/blender_starting_main_settings.txt