Vietnam

Ho Chi Minh city (Saigon)

Take a (public) tour to the Cu Chi tunnels. They're a bit difficult to find but there are some local travel agencies which provide good value. Don't take a private 'taxi' unless you want to spend a lot of money for basically the same thing.
Do travel in rush hour, it's exciting with all those motorcycles.
Charter someone with a motorcycle in a tourist area for a city tour. Make price arrangements first.
Take an umbrella in the rainy season. Travelling is mostly done with motorcycles there's hardly any covered form of transport.