Hoi An is a beach town on the central coast of Vietnam. The main part of the town itself is about 3 miles in from the coast, but the sandy beaches are easily reached by motorbike or taxi. There are a number of really good restaurants here so you can make a real day of it at the beach.
The further away from the big cities like Saigon you get, the more conservative the behaviour of the people. Topless sunbathing is a definite no go area. In fact you may well see people bathing almost fully dressed.
Hoi An is one of the prettiest towns imaginable, especially at night. Many restaurants and bars hang the delightful paper lanterns, for which the town is famous, outside their establishments. This turns entire streets in wonderfully colourful places in which to stroll around.