The Cutaway material enables you to non-destructively subtract geometry from your model.
Simply add the geometry you want to use for the cut, place it so it cuts into your model and assign the cutaway material to it.
You can import simple geometry (sphere, cube etc.) into your scene from the Main Menu, Edit, Add Geometry.
If you only want to cut into some of the parts of your model you can exclude objects from the cutaway. Click the add button and select the nodes you want to exclude. To remove a part from the exclusion select it in the list and click the delete button.
Workaround: Add a groundplane (Edit > Add Geometry > Add Ground Plane) and exclude it from the cutaway.
When the Camera is inside the cutaway object, Color caps do not show and when using Material caps, all objects in the scene will be displayed with the cap material.
Excluded objects have incorrect reflections - Objects excluded by cutaway show reflections of the inside of the object being cut.