Here are various guides from the Vietnam Airlines: 

https://heritagevietnamairlines.com/en/publications/heritage-guide-en/  

We recommend the Foreign Relation hotel: https://fr-hotel.com.vn/en/ (in the city center, near Hoan Kiem Lake and the old district) or Bao Son hotel: https://www.baosonhotels.com/ (15min walk to the VIASM, where the workshop and the boarding meeting are held). Both are 4-star hotels with reasonable prices (single room 60-70USD/night). We will run a shuttle on September 11-13 from the Foreign Relation hotel to the VIASM in the morning and back in the afternoon.
If you want to book a room in these two hotels, please send an e-mail containing your information to the workshop secretary ASAP. Otherwise, you can book online any other hotel in the list that was sent out before. Taxi from the city center to the VIASM costs around 4-6 USD.