A path tracer based on Peter Shirley's Ray Tracing Minibooks
Image from the cover of the first book:
Rendering the image with 100 samples per pixel took 49m 4s on machine with Intel Core i5-4210H CPU 2.90 GHz.
Image from the cover of the second book:
Rendering the image with 10000 samples per pixel took 36h 43m 16s on machine with Intel Core i5-4210H CPU 2.90 GHz.