There are several places where you can post pictures or other artwork, @Hal Pollner . Many people share paintings or just pictures that they like with other members in the Good Morning thread . There is also a section that is dedicated to pictures and videos, and you can start a thread there for pictures you wish to post. If the pictures are of improvements that you have made to your home (you mentioned architecture), then there is a home improvement catagory here in the forum as well. If the painting was historical, then it might be more appropriate in the section for history. Really, it is just a matter of deciding where you think that the picture or painting fits best, and then you can post it there. If you aren’t sure, probably the section for pictures and video would be a safe choice.
I have no objection to adding more designated subcategories. Art is probably too general of a term, as there is an art to pretty much anything. Can anyone think of a two-word subcategory name that could represent what you have in mind? I like to use a Word & Word format whenever possible. I also do things in twos, so I wouldn't add an additional subcategory to "Arts & Entertainment" until I had a second category in mind.