Marble Runs have been bought and lost at my house often. I have had thin plastic pipes that easily fell over and fustrated the kids. I have had insulator foam taped to chairs in order to make a marble run. Now I don't have to have tape on my walls/furniture because I can 3D print pieces into the marble run and snap it into place whenever I like! The kids enjoyed their Duplo again like they never had before. The household transformed into us trying to find enough pieces to make the marble run high and allow the marbles to gain enough speed to zoom through the courses invented.
Of course it is not all roses and butterflies. Some of the hollow pieces didn't print well but instead we have "extended" corner pieces that work great as the marble goes flying down. If we used the regular corners, the marble flew to the ground but with extended wall, it goes down, down at a decent speed.
I found this marble run on Thingiverse. Joachim67 came up with the design for Duplo compatible marble run system. I also printed Duplo compatible marble run cones made by Wuz23. Together it works perfectly!