The basic geometry of the tunnel was created with macros placing individual bricks along a cylinder shape and varying their length using Povray's rand() function.

This was the first real render of the scene, still without photons and quite plain textures. The water already uses megapov's type 1 (fresnel) reflection

I then changed the geometry (added a line of larger bricks on top and changed the bottom part too). There are also photons now on the near part of the water surface. The isosurface bricks have real surface roughness done with a noise function.

I played a bit with the water level and left it as it is here in the end.

Added a rock in the water (done with isosurface objects too) and meanwhile improving water and stone textures.

After some experiments I stayed with this arrangement of the rocks. I also added some variation of the stone texture near the water line.

Here i tried conventional variable reflection instead of the more realistic fresnel (type 1) model. Also started to use a granite pigment function for the stone structure instead of the previously used two layers of noise3d. This is much slower, but more realistic.

Nearly finished now, most important changes here are some fine tuning on the water and the waterline, also improved the quality settings for radiosity and photons.

It still seemed to be somehow empty so i added some flying seagulls as a final touch.

Code for the sky (fairly simple textured sphere):

wt_sky.pov

Code for the water (slightly simplified) and the ground below:

wt_water.pov

Code for a single stone brick including the random variation:

wt_stb.pov