Complete Mountain Level


So I have made a map (attachment) for a level and I’m struggeling with how to actually make this in unreal engine. So I hope it’S clear what part of the map is the way. There is a yellow point. That is the starting point the little black dot near it is the player. So you can see it’s actually quiet a big map. The exact problem is that I don’t know if I should make the ground out of landscape or just meshes because it’s those tunnels except some parts of the map of course.
Is there a good way for doing something like it? SHould I just make a big landscape and cut out the rest of it afterwards? I’m really not sure what to do. It’s really just the ground that I’m struggeling with…

thanks in advance