And I should include this.... This is my absolute favorite museum in the whole world. The American Visionary Art Museum in Baltimore, Maryland.
The artists here are "outsiders" to the art world. People who have mental illness or disability, people who are obsessed on doing their art to the exclusion of all else. People who have never heard of art school 'rules' but rather march to their own drummer in creating what they do. And it's fantastic.
http://www.avam.org/
from the website:
What is visionary art?
Like love, you know it when you see it. But here's the longer definition, straight out of our Mission Statement: "Visionary art as defined for the purposes of the American Visionary Art Museum refers to art produced by self-taught individuals, usually without formal training, whose works arise from an innate personal vision that revels foremost in the creative act itself." In short, visionary art begins by listening to the inner voices of the soul, and often may not even be thought of as 'art' by its creator.