GET ALL THE BIG POES TO OBTAIN THE FOURTH BOTTLE.  YOU CAN ONLY SEE AND KILL BIG POES WHILE AN ADULT AND ON EPONA.  ONCE YOU SEE THE POE, SHOOT IT QUICKLY WITH YOUR BOW AND SHOOT IT AGAIN ONCE IT HAS TURNED BACK FROM RED TO NORMAL. LOOK AT THE MAP BELOW FOR BETTER LOCATION.
 

1) BIG GREY ROCK EAST OF LON LON RANCH

2) TREE NEAR GUERNO

3) TREE AT ENTRANCE OF RANCH

4) SOUTH HYRULE FIELD AT TREES

5) NORTHWEST HYRULE FIELD

6) EAST OF LON LON, V-SHAPED WALL

7) 3-WAY INTERSECTION

8) NORTHWEST OF POE NO.4

9) SIGN IN FRONT OF CASTLE

10) FROM THE TREE OUTSIDE KAKARICO, GO PAST THE 
SUPPORTED CLIFF AND LOOK TOWARDS THE TREE.