Iranians have harvested pigeon guano for centuries by building specially made towers for the pigeons to roost in.
Meybod in Yazd province is home to one of the most exquisite pigeon towers in the country.
It is one of the biggest and the best preservered. It once hosted 14,000 pigeons.

The Meybod Pigeon Tower was constructed in 16th century.
It stands 3 stories tall and is cylindricaly shaped with ridged stucco and brick placements decorating the walls.
It adds to the beauty of the building, but also prevents snakes from sliding up the surface and gaining entry.

Interesting remark about pigeon towers
http://irangazette.com/en/about-iran/iran-history/2-uncategorised/245-isfahan-pigeon-towers.html