This is the current floor texture I've mixed up, I think it's mostly the right amount of weathering for a slab like this, I need to add in more detail to break up the monotony. Every ancient fortress requires mysterious glyphs and carvings, so I will probably break the rooms up with some "granite" blocks embedded in the floor and then add carved glyphs.
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Now that the plan is stabilized I need to start laying out the sub-basement alchemists lab level, and the upper two floors, the ruined bridge level being one of them.