Created with Blender and rendered with Cycles - CPU rendering / 2000 samples / Progressive sampling / Light Paths settings all set to 6. Tile size set to 16x16.
and the magic number... 13 hours @ 2560x1920
This was my attempt to enter the Blender Art Book.. unfortunately, it wasn't accepted (I was so looking forward to the year-long membership) but I guess I still have a lot to learn.. on my own for now.