Here are a few simple 3D shapes for you, useful for level design.
Place them to create gameplay in your level, later replace them with good looking models of a similar shape.
Comes with a block, a ramp and a bridge, as well as rails. All with Colliders, of course.
UPDATE: Now with a pillar and a pillar edge.
Download them here for free.
If you have ideas for more shapes, I’ll update this or collect them and someday make a second package for you.
One problem, the DL is a folder, not a unitypackage, so i cant open it in unity.
Needs more round cylindrical shapes. For stuff like pillars and such
I don’t know what you do wrong, but this is a unitypackage created the standard way. Shouldn’t be a problem to use.
Cylindrical shapes - On their way 
//e: I added a pillar and a pillar edge - see first post.
Other suggestions?
Maybe some types of simple stairs?
I’d always use the ramps to represent stairs…
These models should stay low poly and represent only rough geometry, no details.
Looks useful, thanks.