What is the best way to hang a 3 ft wide heavy Mexican sun clay sun with spot welded bronze rays without any obvious attachment points?

Make sure you are using the correct type of screws if you're attaching it to concrete. If drywall, make sure you are attaching it to a stud inside the wall. Try to get an approximate weight, go to your local hardware store, and ask them to assist you in finding anchors that won't tear the wall, etc.
You may have to drill small holes in the back of the artwork, so make sure you use the correct drill bit.