simtokha dzong (located south of thimphu): located 5 kms to south of thimphu, this dzong is said to be oldest dzong in bhutan which is also known as sangak zabdhon phodrang (palace of the profound meaning of secret mantras). it was constructed in 1629 by zhabdrung ngawang namgyal. inside the dzong there is an institute for language and culture where both monks and common people study. as per the legend the site is believed to guard a demon that vanished into nearby rock which resulted in the name simtokha – simmo (demoness) and do (stone).