Nowadays, sustainable architecture is becoming more and more related to high technology, but this tower approaches from the opposite perspective. Recovering ancient techniques of passive design, by adapting the Persian wind towers to the narrow courtyards of Kathmandu city center, in Nepal, and combining it with moss facades, a conventional building turn into an urban air purifier. The cold water at the bottom of the courtyard stimulates the up-down airflow by negative pressure, while it is oxygenated by the moss, to then be released into the buildings around and in the ground-level facade.