Day trip or weekend trip from Vientiane, Laos?

I'm looking for somewhere for a day trip or weekend trip not far from Vientiane, the capital of Laos.

WikiVoyage doesn't offer anything specifically as it does for many other cities.

The obvious place would be Vang Vieng, but that's a party place for 20-year-old backpackers and I'm now middle aged and I work in a backpacker hostel at home so keen to avoid that stuff.

Luang Prabang looks great but that deserves more time and is a bit far away when you take into account the travel times in Laos.

I know questions of this nature are only accepted on travel.SE if they are specific so here's my requirements:

• Within a few hours travel from Vientiane.
• Not just for partying kids.
• Must have a cheap place to stay, preferably not more than USD $10.
• Relaxing and laid back.
• Any Lao cultural stuff going on or local cuisines a plus.
• A safe place to swim would be a big plus.
• Off the beaten track or not - I'm not bothered whether or not other tourists go.

If it's relevant I want to hitchhike there and back so no tours, stay about two days, and I have a tent and sleeping bag (though I don't know if it's legal for me to use those!)