On the PC there is a Free 3D game engine called Genesis3D which allows you to build games with full physics, lighting, monsters etc. I can remeber the exact URL but you could try: http://www.genesis3d.com Its lots of fun and pretty neat. if you're into coding up your own environments, you could try Crystal Space. I am sure that you would have to do some file conversion to get your landscapes in or you could rebuild using your existing file as a template. Even if it doesn't allow you to import your 3D files, it's still lots of fun and its free and it has a decent GUI (Genesis3D that is).