Custom built concrete birds' nest factories are taking over entire towns in South-East Asia as demand for edible bird's nest soup booms.
This drab, windowless concrete facade does not conceal an electricity substation, data servers, or a high security detention center. Instead, it is a factory farm for edible swiftlet swallow nests, the eponymous ingredient in traditional Chinese bird's nest soup.
The birds traditionally built their nests in the enormous limestone caves of Borneo, from where they were harvested by "skilled climbers using flimsy bamboo trellises." The nests, which are woven by the male of the species entirely from strands of saliva, dissolve in water to give a gelatinous texture to sweet or savory soups and are prized in Chinese cuisine for their reputed medicinal benefits.