Standing Before the Moat                               -      -      - 
(-------------------------------------------------)     W <---(M)---> E
                                                        -      S      -

The field continues up to the edge of the moat.  In your experience
normal moats are full of water, this one seems to break that misconception. 
The moat itself is several hundred feet straight down in a canyon.  You do
not know if the castle was built before or after the canyon appeared but
what you do know is that there is very little chance that any attacker could
ever cross such a divide and live.  Between the archers that could line the
castle walls and the natural barrier before the castle any army would be
hard pressed to get out alive.  You hear the roar of the river as it streaks
by down below.  The canyon and the river continue on to the east and west
from here.