The guard responds, "Do you see that support arch?' He points to a arch of carved metal supporting the stone above, which lies just past the few buildings you see behind him. "Anybody with giant blood triggers it. It will compel you to leave and render you increasingly sick if you try to stay. I was not officially designed to work against giants, but that is its current attunements. Enter the building I mentioned behind me, give your name and reason for entering, and they will place a special arcane mark. It suppresses the mythal's affect on you. Any violence or crime you try to commit will remove said mark, placing you under its effects again."