Quan Su is one of the most important temples in the country. Constructed in the 15th century along with a small house for visiting Buddhist ambassadors, in 1934 it became the headquarters of the Tonkin Buddhist Association, and today it is headquarters for the Vietnam Central Buddhist Congregation. It's an active pagoda and usually thronged with worshipers; the interior is dim and smoky with incense. To the rear is a school of Buddhist doctrine. For good luck (or for fun), visitors of any stripe are welcome to buy sticks of incense and make offerings at the various altars and sand urns. It's easy to just follow suit, and folks will be glad to show you what to do.