The usual spots for tourists to see in Laos are Vientiane for one night, then Luang Prabang and maybe Pakse. But there are many more places to visit. For example, Nam Ngum lake. Okay, the lake itself isn't a highlight, but you can have a nice half day excursion if you do the round trip.
Leave Vientiane on Highway 13 east and follow then Highway 10. On the way, you can make some nice stops.
First is the Lao Zoo. It might be not as big as the ones in your home country, but it is actually worth a visit. First of all, it is a cosy shady place with a lot of trees giving shelter and shadow. Second, the living conditions of most of the animals are not too bad. They have crocodiles and deers, gibbons, bears, many different species of birds. Spend there up to an hour and feed the elephant (yes she is on chains, but as far as we understood during opening hours for security).
After the visit at the zoo, go ahead to the Salt Village. It is a small salt factory on the right where you can see how slat is made in Laos. They actually pump salty water from 100 meter in the ground up to the surface, boil it then in small ponds and then add iodine cause it isn't available in natural salt in this landlocked country. Wholesale price of 10 kg of salt is 10.000 KIP (a bit more than a dollar), so imagine how much they have to produce to make an income.
You heading now to the Nam Ngum Lake (the "ng" is pronounced like the "ng" in "hunger"). Visit the power plant ad take a boat trip on the lake. You can spend hours on the lake, but be aware of changing weather conditions. After, have lunch at one of the restaurants there. Since you are at a lake, fish should be the dish of your choice.
Rest a while and then head back on Highway 10 until you reach Highway 13 again. Turn right north then. The Coordinates are roughly, 18.448021, 102.419357, look for the Ban Phon Hong village. If you don't have a driver/guide, try to ask the locals for the way to the caves. The last few meters you have to walk since it is hidden in the forest. Be careful during rainy weather.
After this visit, turn back to Highway 13 and go south about 63 Kilometers back to Vientiane.
If you don't want to go by yourself, you can book this trip also through Diethelm Travel (go to the office at Nam Phou Square in Vientiane)