according to your map... there's a rat in the north-west (red) room, and 2 rats in the south-east (blue) room. the way i did it (from the main entrance) is thru the sides (behind the hedges), all the way to the back. up the ladder thingy(green-structure) which will bring you to the northern balcony. once you're on the balcony, go to the north-western (red) room and kill the rat. after that just get yourself caught to respawn downstairs. climb up again and go to the north-eastern (red) room. wait for both guards to go outside to the balcony to go to the south-east (blue) room. *if their timing is such that only 1 guard goes out at a time, wait for the guard closer to you to go out. the other guard (though facing your way) shouldnt be able to catch you.