Small flattish terrain, lots of sky - some pointers please...

Hi - new game dev ( haha ) - but long time developer ( too many years! ) . Anyway, I am just after a few pointers about the approach I need to take ( not to have it solved for me ). 3D base building game ( not the most original idea - but i am not using the asset pack). The scene is set inside a large crater. My camera will be a child object of a game object that floats directly above teh center of the base - which allows me to easily pan around the base by rotating the centred game object. all good. Now the terrain - as the 'action' takes place inside a crater, i want lowish crater walls ( no problem ) but then not much beyond that - i basically want the crater walls to be the horizon and the sky to meet those walls, so i don't need my terrain to go much further than that. Do i use a 'plane' or a 'terrain'? If I use a terrain, I can't seem to get the area beyond the terrain to be 'nothing', letting the sky be visible. All I want the camera to see is either inside the crater, the crater walls, or the sky. I have tried to make this make sense - not sure it does. if it doesn't get any hits I will try and reframe it differently with pics - but here's hoping!! thanks all. ( I am a much better developer than I am a question asker on forums - honest! )

 

Skybox. Skybox is the answer. Wow.