I've got a plan! The lower deck (partially shown here) will be marked off and painted as a 12' chess/checker board, I know where to get a bunch of appropriately sized flower pots (cheap!) which will be painted predominately black or red but with whatever a kid's intuition wants to do with it. May need to trim the lip of the pot with duct tape (note to self, look for colored tape) in order to cushion the 'checkers' as they move around the concrete board. The drainage hole will be used as a finger grip to pick up and move the 'men'.
Later, the checkers can be used as pawns and I'll find larger pots to paint up as appropriate chess pieces. (Any creative ideas appreciated!)
The chess board will take up less than half of the available space, so I found a gridded labyrinth design (simplified) and will save that for another time... maybe later this summer. Would be fun to read and study on the history (kid's view) of labyrinths while we paint it.
Also found a bunch of nearly new straw hats at the local Thrift Store (a favorite place to shop for surprise finds) so that's something else the kids can paint. Maybe we'll have an Easter Parade ;-)