here's an example.

the mesh on the left is the original. very simple and made with snap to grid to get an even appearance. the middle one has one level of subsurf applied and the one on the right has two levels. the one on the right may be a little too high-poly for some, but the middle one is pretty safe. to make these kind of shapes without subsurf would be hard work, this way is a lot easier.
subsurf-tunnel-demo.blend