Derek and a sousaphone.

First part of the dream, there were big spider robots behind the house. Derek, from The Sarah Connor Chronicles, was there. He was very disappointed at me that I hadn't brought a gun. I went back into the house, which was filled with glass objects and rocks, like the shiny-stuff store. I found a little handgun and went back out. The bullets had no effect, and Derek was still peeved at me.
Second part, escaping from a boarding school. It was a Christian boarding school, and the chapel looked like St. Peter's. The pulpit had turned into what looked like a conch shell, or a sousaphone. We had to climb through it to get to our secret tunnel we'd dug to escape.