Rinpung (Paro) Dzong is a fortress-monastery built atop a limestone promontory overlooking the Paro river. Its naturally defensible and strategic location provides panoramic views of the Paro valley region. Although constructed in its current form in the mid-17th century, the site's history extends back into antiquity.

According to popular legend, the site was visited in the 8th century by the Tibetan guru Padmasambhava, commonly known as Guru Rinpoche. The Tibetan master saw the high limestone base that would one day form the foundations of the dzong and dubbed it "Rinpung Drak" (i.e., "cliff of the heap of jewels"), from which the dzong obtained its current name.

History comes into sharper focus in the 15th century with the arrival of Humrel Dung Dung Gyelchok, a Buddhist notable who had studied at the storied Ralung monastery in Tibet, the wellspring of considerable Drukpa Buddhist talent in Bhutan. One day, while meditating in the Paro valley, a pernicious deity attempted to distract him with earthquakes and waves upon the water. However, the god was no match for Gyelchok, who used his esoteric knowledge to trap the entity and convert it to the Drukpa cause, thereby transforming it into a guardian of the valley and the Buddhist dharma. Gyelchok built a small shrine at the top of the cliff in the deity's honor; this crude temple was later enlarged to become a five-story temple. Hungrel Dzong, as it was known, referred to the cliff's alternative name, Humrel Drak, bestowed by the Tibetan polymath Thangtong Gyalpo (1385-1464), the "King of the Empty Plain." He is credited with temporarily driving the deity out of the cliff (in an earlier decade) by uttering the mantra "Hum."

The Humrel Dzong was apparently in good order when Ngawang Namgyal (1594-1651), the grand national unifier of Bhutan and the first Zhabdrung Rinpoche, first arrived in Paro in the early 1640s. By that time, the Zhabdrung was already firmly in control of much of Bhutan, having prevailed at the Battle of Five Lamas in 1634. The local rulers of Paro handed over control of both the dzong and the entire valley to the Zhabdrung and his nascent state. As the Zhabdrung had sufficient authority to requisition the finest materials, his architects tore down the old Hungrel Dzong—which was largely made of rammed-earth walls—replacing it with a far larger stone structure. Construction took some five years, resulting in the current form of the monastery that we see today. Perhaps to differentiate it from the former structure, it became known as Rinpung Dzong.

Reference: https://www.orientalarchitecture.com/sid/1550/bhutan/paro/rinpung-paro-dzong