Occasionally, I stumble upon some fractal formulas that match in strange but beautiful ways. This image consists of only two formulas, HalfOct4b and Riemann2, but they merge nicely. This resembles some sort of Victorian basement structure which infuses a decent horror in its shapes to me.
The lighting was tricky in this image. To get the hazy glow effect from the top, I first rendered the light at a different position, calculated the soft shadows and then moved the light torwards the camera before saving. Otherwise the image would have been completely blown out. No fog was used for this.
Rendered in Mandelbulb3D, afterwards some light enhancement in PS.