Hoi An, once known as Faifo, with more than 2,000 years history, was the principal port of the Cham Kingdom, which controlled the strategic spice trade with Indonesia from the 7th to the 10th century and was a major international port in the 16th and 17th centuries - and the foreign influences are discernible to this day.
The culture & heritage is mostly from the Cham people whose kingdom originally stretched from Hue South to Phan Thiet (South of Nha Trang) - the Champa's most likely originally from Java. The original Cham political capital was Tra Kieu, the commercial capital was Hoi An and the spiritual capital was My Son (Hindu). The Cham people were Hindu, and by the 10th century the influence of Arab traders to Hoi An resulted in some converting to become Muslims.
The second major influence was from the Chinese, firstly from traders but especially the escaping Ming Dynasty armies who after settling in Hoi An for some years moved further south and created Saigon as a major trading port.
The third and last major influence of culture & heritage was from the Vietnamese and is fairly recent and only came after the Cham lost control of this area. For a tourist wanting Vietnamese culture & heritage, Hue is a much better destination than Hoi An (but the weather is much rougher too!).
While the serious shipping business has long since moved to Da Nang, the heart of the city is still the Old Town, full of winding lanes and Chinese-styled shophouses, which is particularly atmospheric in the evening as the sun goes down. While almost all shops now cater to the tourist trade, the architecture has been largely preserved, which is unusual in Vietnam, and renovation has proceeded slowly and carefully - it's mercifully absent of towering concrete blocks and karaoke parlours.
The culture & heritage that UNESCO World Heritage Site status for Hoi An Ancient Town was trying to preserve has long since gone. Since 1999, when UNESCO WHS status was awarded, there has been a massive increase in tourism - with the result that most houses have been sold by the community to speculators and shop owners to be used for commercial purposes. The former community, and with it their culture and heritage, has gone and in their place are endless indistinguishable shops, restaurants, art galleries, etc. There are literally hundreds of tailor shops in Hoi An.
UNESCO Biosphere Reserve status also applies for Hoi An Ancient Town, but in reality this status, like many other UNESCO statuses, is not being cherished by site management.
The main thoroughfare in the Old Town is Tran Phu. Just south of the Old Town, across the Thu Bon River, are the islands of An Hoi to the west, reachable via Hai Ba Trung, and Cam Nam to the east, reachable via Hoang Dieu.
Hoi An is known for clothing and shoes, with more than 600 shops catering to a very limited pool of tourists. Walk some of the streets outside the old town and you will see open-fronted workshops operating all hours where the clothes are made.
(Source: https://wikitravel.org)