I drove through Hoi An four or five times in 1972 on the way to a construction site five kilometers beyond Hoi An on the coastal beach. We had contracted with a Vietnamese contractor to build 100 units of family housing for Vietnamese navy families. I had no idea at the time of the architectural and cultural significance of this town, although I noticed that it was very picturesque. We usually drove past the town on the waterfront, but sometimes boarded a VN Navy PT boat at Hoi An quay for transportation down river to the coast. The town was otherwise a very quiet place.
No more. Hoi An has since been declared a World Heritage Site and is now mobbed by tourists. Check any tourist guide for a complete discussion of the reasons. Essentially, Hoi An is a complete and concise exhibit of Vietnamese, Chinese, and French Colonial architecture and culture all in one. The town was originally a Chinese fishing village, and the town retains the "congregation" assembly buildings (or temples to ancestors) for the major Chinese cultural groups (Cantonese, Fukienese, etc.).
The rain let up long enough for us on 9 October for us to have a good day's walk around Hoi An, which is still a small town. On 10 October, it rained all day.
Here is a picture from the Hoi An waterfront in 1972. At the time, I thought the water was a bit dirty for the kids to be swimming in.
Here is a picture from the Hoi An waterfront today, and the water is substantially dirtier now.