Dicht = 
      Plot3D[x^2 + y^2 + Sin[x*Pi], {x, -2, 2}, {y, -2, 2}, 
        PlotPoints  ->  30, Mesh  ->  False]

Linien = 
      Plot3D[x^2 + y^2 + Sin[x*Pi], {x, -2, 2}, {y, -2, 2}, 
        PlotPoints  ->  10, Shading  ->  False, 
        MeshStyle  ->  {Thickness[.005]}]

Show[Dicht, Linien]

\(Plot3D // 
	Options\)