Punakha Dzong

If you only have time to visit 1 Dzong, I think this should be the one.

Besides the fact that so many historically significant events are hosted here e.g. the king's coronation, the founder of bhutan ruled and defended multiple attacks from this fort, temple that holds the embalmed body of the bhutan founder, etc

The architecture has so much details. The inside of the main temple hall is amazing.