The cylindrical building was built in 1641 AD. by Desi Tenzin Drukda, the then Governor of Paro, as a watchtower to look over the Paro Dzong in case of invasions from the north. As was the situation in those days, invasions were occasional and the Dzong, which was the center of administration in the state, needed to be overlooked by such towers to look out for invaders. The unique structure has six floors that go spiraling down from the top. During the olden days the building not only housed soldiers but also prisoners of war, mostly invaders.