The turtle is called Shen-zin Shu or the Wandering Isle (World of Warcraft). It were a normal turtle but it began to grow alot. A pandaren (the Warcraft pandaren-like race) befriended it and he and the turtle left the Pandaren homeland of Pandaria for adventure. Soon others joined him as the turtle became so large it could hold villages and mountain ranges.

First I thought it was discworld, then I thought, it was a turtle island island, then I notied the extra legs, and came to the same conclusion as you: Giant Spider turtle! Also, very nice build, Divici! appears to be fom worldf warcraft according to desc?