It is a nice looking technique that uses many, yet easy to find bricks to achieve a rounded effect.
-1x1 round bricks, for support
-any smooth 1x1 brick (cone, round, normal, headlight...)
-something to SNOT the SNOT (technic pins work, but the numbers get really ugly that way)
-some 1xX bricks to give the tower/platform some length in the Y dimension
-a lot of 2x2 tiles in primary colour
-(optional) some 1x2 tiles in primary colour and some in a secondary colour, to break up the monotone wall (note that secondary colours are used mostly to add detail to smooth surfaces, our example has accents because it is a part of a castle with some smooth walls, not because it would "need" them)
-A monthly supply of tranquilizers