An INNER COURT is any open area, other than a YARD or portion thereof, which is unobstructed from its lowest level to the sky and which is bounded by either:
(a) BUILDING walls; or
(b) BUILDING walls and one or more LOT LINES other than a FRONT LOT LINE; or
(c) BUILDING walls, except for one opening on any open area along a SIDE LOT LINE or REAR LOT LINE which has a width of less than 30 feet at any point.