Fly from Amsterdam to Hanoi and then from Hanoi to Da nang ,
Spend 9-10 nights of beach time in Da nang , meanwhile going on day trips to Hue and Hoi An;
Then move to Siem Reap by plane and then explore Angkor watt and surrounding temples for the 2 days
Then go by plane to Hanoi and then head to Ninh Binh for 2 nights where explore Trang an and Tam Coc regions mainly by boat and also have some hikes
Then go back to Hanoi, stay there 1 day and then go see the Ban Gioc waterfall at the Chinese border( this tour takes 2 days and one night) - better to do it with the organized group for the simplicity of the logistics
Fly back home on 24 of March