Maps vs World in Unity

I have one more question. I just start with 3d web development so maybe i have nub questions but i need help :) i am going to build game with dynamic world, for now i know some answers about how to locate dynamic thing on the map but.

i need create island with caves, building and user will be able to enter to it. i think caves will be just different location, also if island is a very big location i think need to divide it to different locations? and then dynamically load it? maybe some one have good tutorial about it? thanks

Unity’s terrain can’t use caves if you want caves you either need to use unity’s terrain and add a cave entrance that loads a new level when you click on the entrance. Or Make a world in a modeling program like blender. Cause with a 3D mesh your world could have as many caves as you wanted. NOW heres the catch with the second option your going to have lots of lag in your game cause the world is one large mesh with lots of caves and the game has to render all of them, but thats the price you pay for having every thing in one scene. But if you use the first option then you save lots of memory.