As consider the holiest sites in Vietnam they have a dress code: it is not allowed to wear shorts and sleeveless shirts (as the weather in this time of the year is too hot a scarf is a good option to cover your body). Cameras is not allowed they collect all cameras before you enter the mausoleum (so if you have a massive one just live it in your hotel or in the luggage storage place). While you are inside, don’t talk loudly and take off your sunglasses and cap. Admission into the Mausoleum is free.