A logarithmic spiral of perforated spheres, created using Superflow maxscript in 3dsmax. Exported to Octane render, and rendered using the Direct Lighting/Diffuse kernel in about 30 min on my Nvidia Geforce GTX 660.
I am _so_ far behind on my subscriptions that I'm just going through the whole stack image by image with no indicator of what group or artist an image comes from. I still knew right away that this was yours. I really like the DOF, though I find it a bit artificial where it gets extreme.
It's GI. Octane just has several types of algorithms to solve GI. Pathtracing and PMC are unbiased. The Direct Lighting, is the term they use for biased GI solution.