Uh-oh, now you guys are trying to confuse me. I'll try to answer the best way I can.
Is it solid? You know, I had to look this up... I started to have doubts. And I was right, because I found out it's not really solid. However, I think most people in the world don't know about this and think it is completely solid.
Can you walk on it? No.
Is is a proper noun? Yep!
Is it made of only one thing? No.
Can you touch one? No.
Can you stand/walk on top of one? No.
Have you ever seen one? (in person, I mean ...not in TV programs, movies, on the Internet etc.) In person? Not usre what you mean, but NO.