Okay, I can’t really test it, because the scene is too heavy for my computer, but the problem is (I think) that your Irradiance Volume is too dense, or too be more precise: there are light probes inside your columns and below the floor and above the ceiling and so on. This causes the shadowy artefacts. (I’ve tested it without all the complex Shaders and they were still there).
I don’t use Eevee myself if I can avoid it, but @jlampel explains it really well in the Fundamentals of lighting.
