The Dark Citadel

Going for a dark and evil black stone citadel. I love the gothic cathedral architecture which looks spooky and sinister in my opinion. Also the mordor architecture like Barad dur, Minas Morgul and the black gate from the LOTR films.

Does anyone have advice for pulling off obsidian-like stone without losing all the detail? It always turns out weird for me.

Anyway here are the outside support columns pretty much done:

Reminds me of Half Life 2