As my first stop in Laos I visited Luang Prabang, the former capital of Laos. The main components of the site are situated at the confluence of Mekong and Nam Khan rivers.
The town boasts several temples, some French colonial buildings and the former royal palace, albeit that last one is rather amusing than impressive. My highlight was the Wat Xieng Thong temple. And the overall relaxed mood of the city.
Getting There
Luang Prabang has some domestic flights. It has also a few international connections to China, Vietnam and Thailand. My impression was that it's actually better connected internationally than the capital, Vientiane.
Apart from the flights there are also busses and the more touristy mini busses taking you to most parts of the country. Specifically, Luang Prabang is the closest major town for Phonsavan and the Plain of Jars.
While You Are There
I think the town can be visited in half a day (or even a bit less). Still it would be a pity if you left early. Plus, the bus connections may very well force you to stay at least a night.
You have plenty of good restaurants to choose from in Luang Prabang. The town also offers Laotian cooking classes and daily yoga classes. Only isssue I had that it get's really warm around noon so it's not a good time to stay outside and move around.
If you plan to venture outside (I didn't) there are daily boat excursions to the Pak Ou cave. You can also go via tour or by shared cab to the Kuang Si Waterfalls.