Walls Object [Excel 2003 VBA Language Reference]
Represents the walls of a 3-D chart. This object isn't a collection. There's no object that represents a single wall; you must return all the walls as a unit.
Using the Walls Object
Use the Walls property to return the Walls object. The following example sets the pattern on the walls for embedded chart one on Sheet1. If the chart isn't a 3-D chart, this example will fail.
Worksheets("Sheet1").ChartObjects(1).Chart _ .Walls.Interior.Pattern = xlGray75
Parent Objects | Chart Object