The Black Citadel

After walking without interruption for about half an hour, the trail slopes down a hill and bends around. A large open clearing in the forest is visible just ahead and you approach cautiously. You notice a black horse grazing in the middle of the clearing, but then you notice it has a horn. A black unicorn! A very rare breed of unicorn indeed. You've heard black unicorns can be very dangerous when threatened or not respected. What should you do?