That is ash with the lye that comes from the wood to the Cham Islands which might be close to 12 kilometers through the Coastline of Hoi An. source: citypassguide Hoi An’s Japanese Covered Bridge, dating again to your 18th century, is One of the more iconic attractions in Vietnam. https://hoiinan06048.bloggip.com/35032509/facts-about-hoiinan-revealed