HaunterV wrote:First steps are taken where exactly?
In a modeling program. Probably the best free modeling program out there is Blender, check it out:
http://www.blender.org/
For textures GIMP is recommended (if you don't want to pay):
http://www.gimp.org/
Here is a good texture site where you can find almost anything and turn it into absolutely anything with a bit of image manipulation:
http://www.cgtextures.com/
You could of course simply stack existing walls/pillars etc. Would be the easy way to do it (only a minimal amount of learning required to do that and probably takes less than an hour for a whole tileset), but that certainly wouldn't look very impressive.
Personally I would use larger textures for a huge tileset to keep the pattern effect at a minimum, like 1024x2048. That will be the biggest problem you'll face with huge walls like that, even though in Grimrock you can't see very far, which is good (in this case). Plus in Grimrock you naturally have a pattern effect, so as long as it's not too bad it doesn't matter. Other than that it would be similar to the Prison tileset, only with even higher walls.