How to make a closed terrace terrain from contour curves

Nope - my Grasshopper graph makes a smooth mesh surface, not a terraced one - so party on!

Here’s the Rhino 6 version. Note that there is a file converter that you can download here:
https://discourse.mcneel.com/t/rhino-3dm-file-version-converter/

2021-05-05-Situationsplan_3d_Skissmodell_wd-RH6.3dm (4.9 MB)
-wim