Dalat and the area around there in the highlands is a very popular destination for the locals, not as much for foreigners. Well worth a visit. Incredible variety of food, very helpful, friendly people. You don't need ac or a fan.Best spots, things to do. Not necessarily typical tourist areas.
Easy to get back down to the coastal towns and the railway
If you are going south the Mekong Delta is good. Travel to a few towns there like Tra Vinh and make your way to Ha Tien. Small town on a river. Can go to Phu Quoc from there. That's very popular with the locals who want a beach destination.