My friend and i had a great experience of stay when staying Serene Boutique hotel, staff are very friendly, rooms are tidy, the location is convenient, and the breakfast were good! We visited Vietnam for 6 days but stayed in Serene Boutique for only 2 nights, but they were very nice and borrowed us the bathroom in their spa for us to take a shower before taking night bus to sapa.
Furthermore, i left my shoes on the bus when leaving Ha long bay, the receptionist Zoe was very kind to help me to contact the local tour office, and i got my shoes back 2 days after!
If you are looking for a great hotel in Hanoi, i would highly recommend Serene Boutique Hotel!