Public buses run several times from the capital city of Vientiane to Vang Vieng along the paved Route 13. The public buses are usually quite crowded and without fans and AC. They are however, among the cheapest ways to reach Vang Vieng from Vientiane. Once the seats fill up small plastic stools are offered and are placed down the aisle in order to accommodate more people. This bus makes one bathroom stop about 1/2 way between Vientiane and Vang Vieng. The stop we made was just on the side of the road. Any luggage or gear is tied down & stowed on the top of the bus or in compartments on the buses side.
AC mini buses also run between Vientiane and Vang Vieng. You pay a little more but to me the AC is well worth it. They also shave about 1 hour off of the time it takes the public buses to travel the same distance. The reason being that these buses do not stop as much as the public buses.
You will need to acquire a visa to enter Laos. You can secure visas these days electronically or on arrival at the border or airport. Bring an extra passport photo or two and have a reservation for lodging already secured (the name of your guesthouse or hotel will be required when filling out the visa paperwork).
Getting a visa at the border is a fairly painless process. It takes maybe 20 minutes or so depending on if there is a line or not.
If you enter Laos from Nong Khai in the north of Thailand expect your crossing over the border to take about 60 to 90 minutes. The reason is there are several check points between Thailand and Laos – and there is limited transportation between these checkpoints. In other words, you have to wait for a government bus to transport you between several of the checkpoints.