Plenty to see in Hong Kong, just google all the ideas and easy to get around via taxis and train. We even tried the bus, but got very lost and saw parts of Hong Kong no Westerner has ever seen before.
Halong Bay is just beautiful....do one of the boat tours, its a spectacular part of the World.
Ko Kood if the very BEST of Seabourns Caviar in the Surf....gorgeous beach.
Bangkok and Ho Chi Minh are very busy Cities, but again lots to see, I would only do these places on a Tour, as I'm not too adventurous these days. I'm sure there would be tours that would be of interest.
Don't think we got off the ship in Da Nang, I seem to remember it being a very wet day so we had a lazy one onboard.
And Singapore is one of my favourite Cities in the World, again lots to see, just google to see what interests you. Also has to be about the safest place in the World......we were once going to eat in a very very busy Food Court for local food.....as soon as we spotted a spare table, we grabbed it, then took it in turns of going off to collect our food. Couldn't believe our eyes when a group of young girls came in, put their purses down on an empty table, then all went off to look for food.....10 minutes later, they were back and their purses were still where they had left them Imagine that happening ANYWHERE else in the World? Really nice place to visit.