2.5D terrain? (Hungry Shark like)

Hello, I am working on a 2.5D game.

Using the terrain from Unity, I can do a well looking terrain, but the problem is that the up part of this terrain is unlimited, and as my character is able to fly, I would like it to be limited in how high it can fly, and would also like to be able to make caves and such.

What I am looking for is basicly a way to achieve this:

alt text

As you can see, in this image the shark won’t be able to go up the limit of the cave, but it’s the terrain is still in 3D.

Maybe you’ll understand better if you check the map of this game:

alt text

As you can see the map is 2D, while the game is 3D.

Does anyone knows a way to to this? Thank you!

Model your terrain in, say, blender, 3dsmax, or maya, and import the mesh into Unity.