If you've ever been in a real cavern, you will immediately see a need for multi-tile cave columns, as well as "forest" column formations. I have been in many caves, and they are so wondrous and varied. I have been very slowly working on my own underdark tileset, which I refuse to show anyone until it is finished. It is currently un-roofed, but it does have raised sections which hold water. I wish my real life pictures did the topic justice, but the lighting is all wrong, and I was not skilled in the use of my camera in the dark underground at the time.
Another thing I have had issues with is finding the correct textures and colors to represent the various matrix into which the cavern system forms. But I have come to the realization that the only texture you really need is frozen flowing water...recolored! The outcome is the same, only the color and level of transparency is different. Karst caverns hold many other natural wonders which would be easily represented by low poly tile additions, or even placeables, such as boxwork outcrops, or cave bacon. The textures on those two alone could be so simple, that they would not even need anything more than a repeating brown rainbow for one, and simple cross lines for another.
If I could suggest anything at all in helping cave columns, stalactites and stalagmites get created for NWN, it would be to simply start with a picture or simple texture, and then build out from the texture in the same manner that I used for creating weapons from 2D screen shots. Nothing could be more easy, and your columns should come to life very quickly. Just be sure your final texture is flatter than a flash filled picture you would expect from a newbie photographer in a 300 foot deep dark hole. If I could suggest a flatness level for your texture, I would directly point you toward those used for this month's custom content by Shemsu-Heru. There should be no diffuse shiny bits unless there are actually crystal faces you wish to over-represent. In the case of shine from wetness, let glossiness/shine factors do it in the engine for you, but do not use metallic shine/transparency if at all possible. Environment maps should be black, or a very dark version of the color of the surrounding matrix, especially on water. If you have ever seen water in a black cave, you know what I mean. It is creepy beyond creepy to me.
I have very few textures I am currently willing to share in this department, until I am finished at least, but I hope that encourages some texture artists out there to run with my examples and pointed-to information.
