How did they do it: Trine 2.5d terrain?

Question

How did they make the terrain in trine? I think they took a polygon approach. It doesn't seem that they used a heightmap because it is in all three vectors, or a voxel method because it doesn't have overhangs and cliffs. If it is polygon-based (I assume it is), how in the world would you texture the whole thing?

Notice how it's not very symmetrical and has lots of depth:

Answer 1

They use the same models again and again in Trine. They use a lot of batched rendering. Because of their unique camera angle, a lot of the meshes get culled with frustum culling.

The levels are hand-made by artist. They are just very good at re-using the same models over and over again.

Answer 2

It looks like any regular 3D model. The only thing that's "2.5D" about it is the fixed camera and play space.

Answer 3

The terrain is built as separate meshes by the artist, and possibly have a separate level designer to place the meshes for making the levels. They are just so well-modeled to give the impression that it's one continuous terrain.

In some respects it's really a 2D puzzle action game, making the design and programming of the game logic easier than fully 3D games. The level designer is restricted to just placing the objects along a 2D plane.