On a Sunday afternoon. we were heading past the McMaster University Medical Centre when I saw in the sky what first appeard to be a helipcopter hovering above the building. I thought it was strange as I was not aware they had a helicopter pad. It also became apparent this object had no tail rotor. By this point my friend had crossed the street and was also pointing out the object. It appeared to be metallic, as the sun was reflecting off of it. It also made a high pitched like nice, and at times would shoot off at great speed. We followed the object for a good 15 minutes or so, and at times it seemed like the object was aware of us, at disappearing then coming back into our view. After some time following it I was moving from total curiousity to some apprehension as we seemed to be following the object into an enclosed part of the hospital. But then it flew up rapidly and was gone.