Adding my experience having just done a week in Laos. We were visiting friends in Vientiane, otherwise there really isn't much to see there and I would skip. The Crowne Plaza was lovely though, and the connected brand new Holiday Inn looks nice too. The new Doubletree is more in the heart of downtown, but we ended up taking a lot of Locas (Laos version of Grab/Uber) regardless as the sights are pretty spread out and the weather isn't great for walking.
Train to Luang Prabang was super easy. We were traveling the day reservations opened for our train, so we paid a service to book for us. Yes the train is far outside town. Security was a nonevent. We were worried about some small aerosols in our suitcases but no issue. Some people with bigger ones got flagged by the x-ray. The line is right when you enter the train station so can get backed up at entrance but there was not a meaningful wait. No wifi on the train or in the train station, but there are some coffee shops, a dairy queen, a juice bar, and a minimart.
Luang Prabang train station
Train itself was comfortable, we paid the extra for first class (below business class). Attendant came by selling snacks. Nice views of the mountains, and we had about a 15-min delay.
In Luang Prabang, there was also a long drive to the city but our hotel (MyBanLao) provided a van to pick us up. We were happy with the location of the hotel, which allowed a 15-20 min walk to the old town, or a very quick ride in one of the hotel vehicles. A lot of the more sprawling and high end hotels are further out, making it harder to enjoy the charm of the town itself, which we found to be the highlight of the visit.
Luang Prabang old town
Luang Prabang sunset
In terms of activities, we did a bamboo weaving class at Ock Pop Tock, which we enjoyed and is in a stunning location on the Mekong. We did a Kayaking trip to the Pak Ou Caves which weren't particularly interesting. We arranged a driver with our hotel to the Kwang Si waterfalls which were unfortunately low due to the rain. Definitely leave early if you go; we had the place almost to ourselves when we arrived around 8:30, but by the time we were leaving it was packed to the gills with tour groups.
We really enjoyed a sunset cruise on the Mekong, as well as cocktails watching the sunset and some excellent meals in town. The night market is very similar to that you see all over Southeast Asia, though focused on crafts. We flew directly to Hanoi from Luang Prabang, and the airport is small and relatively easy to navigate, though we arrived at the same time as a difficult tour group that seemed to have booked every other seat on our Lao Airlines flight.