The Punakha Dzong is a beautiful piece of architecture. The temple within the site is impressive with the various magnificent Buddhas. The views from the Dzong is also stunning given that Dzong is at the point where the female and male rivers meet. To get there you have to cross a beautiful bridge which when you are in the middle of the bridge gives you great view of the valley.
The Punakha Dromche or Tshechu Festival falls on early spring and this is best time to visit with all purple Jacaranda Blooming with other beautiful flowers like Rhododendron, Bottle Brush, Bougainvilleas to name few and many more.
The attraction is free to public and required to produce your Punakha permit (for Indians) while entering, so keep it handy. There are many monks inside who meditate and offer prayers. Except the prayer hall, all other places are allowed to be photographed.
The winter timings are different than summer timings. Wear dress appropriately "full sleeves" and "full pants" no shorts allowed.