Round, canvas, fancier than a tent, but more rustic than a house. It's a yurt!
Yurts in Oregon State Parks sleep five people, and have heat and electricity plus an outdoor fire pit and picnic table. As with camping though, you'll need to bring your own bedding and dishes. More than a dozen coastal and four inland parks rent yurts year-round, with rates between $27 and $30 a night. You can find yurts to rent in other places—including California, Hawaii, and Costa Rica, among others—as well.