The ornamental design for a spaexterior, as shown and described.
FIG. 1 is a perspective view of a spa exterior showing our new design;
FIG. 2 is a top plan view thereof;
FIG. 3 is a bottom view thereof;
FIG. 4 is a front view thereof;
FIG. 5 is a back view thereof;
FIG. 6 is a side view thereof; and,
FIG. 7 is a side view thereof.
The broken lines immediately adjacent the shaded areas represent the bounds of the claim, while all other broken lines are directed to environment and are for illustrative purposes only; the broken lines form no part of the claimed design.