Anything that detailed and large is going to be done as a mesh, not a solid.  Getting the correct curves would be especially hard for a solid.  Even a mesh will be triangulated with hard edges until you take it into software which allow you manipulate edge smoothing (at least, the appearance on screen).

Getting a surface from contour lines is tricky.  One method is to take sample points along the contour line at intervals (typically much less than the contour interval), after which the points can be triangulated to form the surface.  You can still end up with some artifacts and not very pleasing appearance, as the faces will be "striped" along the contours.

Is there any specific requirement for this to be a 3D solid?

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