Mekong Delta
River towns, orchards, and floating markets south of Ho Chi Minh City, plus the island of Phu Quoc off the southwest coast.
The delta is rice, water, and fruit. A day tour from Ho Chi Minh City reaches the near river towns. Can Tho and its floating market are better with a night there, because the boats are on the water early.
Phu Quoc is an island trip, usually a flight, not a delta day tour. It shares this corridor because that is how people leave the city for the southwest, not because you can see both in an afternoon.