This is certainly the most complicated scene I've even drawn, and technically it counts as MLP fan art too. :-] It's a commission for Sharpfang of the city of Entwine, the capital of the zebra kingdom in the setting of his pony stories. The story, upon which this is based can be found here:

http://www.fimfiction.net/story/34781/Prince-of-Zebras

Entwine is built in a deep long canyon in the desert, but centuries of careful gardening, rock carving and harnessing of the few native vine species have allowed the zebras to create a lush city with a moist environment and lots of plants and gardens. A giant, very strong and slow growing vine known as Iron Ivy forms the skeleton for bridges and other supports, while other varieties of vines grow on and around it providing fruits and forming a canopy which shelters the city from the harsh sunlight and winds of the desert above.

In fact only slums occupy the land above the canyon, while most of the city proper is carved into the canyon walls and the bottom is occupied by public buildings, parks and luxury homes.

It was quite fun to design the city given the specifications, I started thinking of Mesa Verde but as I looked for ideas I stumbled upon many other weird cities carved in stone which are found around the world, especially in Turkey... humans live in really weird places sometimes. o_0

By the way Princess Celestia is currently visiting the city, and can be spotted if you look really carefully...