When I traveled from Busan to Australia, I had a layover in Ho Chi Minh City, Vietnam. I booked a flight with Vietjet because it was cheap, but they unilaterally canceled it, so I had to rebook with another Vietnamese airline. Vietjet refunded me with a credit that had a six-month limitation (how did they expect me to use it? Also, I couldn't even give it to someone else). Since I didn't have any travel plans within that time frame, I felt like I was scammed out of $150. I didn't receive any help from the travel agency, Trip.com, and I haven't used Trip.com or Vietjet since then.
Putting this depressing story behind, the best thing I had in Ho Chi Minh during my stopover was, of course, Sinh To, a fresh fruit smoothie. I heard they only use fruit without any water, and it was truly delicious. I've tried to find something similar in Australia but failed every time. Before my departure, I also visited the pink church by calling a Grab taxi. The taxi driver kept talking about football manager Park Hang-seo.
The streets filled with motorcycles were quite impressive, and if you ever travel to Vietnam, Grab (similar to Uber) is a must-use!