From the blog Sanctuary Of Random Keystrokes:
Trongsa was the first dzong that I have ever entered so I have a lot to tell. Our description of visits to other dzongs will become less detailed and will state only what is unique to each one.
It was a sunny but cold morning in Trongsa. We checked out of our guest house and went straight to the Trongsa dzong. As we neared the dzong, our guide took out a long white scarf and wrapped it around himself. The common public must wear one before entering a dzong or face stiff fines. Tourists are fine – even in jeans.
The dzong was as beautiful as it was imposing. We entered through a large wooden door with the wheel of dharma painted on it. In its center was an ornate door knocker. It is a motif we’d see consistently on most doors across the dzongs.