Recently, I was tasked to help create multi-level main navigation within the master page of a website. After a little investigation and finding that the CSS List Menu would not work for my implementation, I concluded that it would be the perfect opportunity to use either a Universal Viewer or a Universal Viewer with custom query; both of which I implemented with Hierarchical Transformations.
I. Universal Viewer
Add the Universal Viewer web part to your master page, set the appropriate content and content filtering properties (just as you would for a CMS Repeater) and then check the boxes for Load hierarchical data, Use default hierarchical order and make sure that the Hierarchical display mode is set to: Inner. Select the 'OK' button and navigate to the Site Manager to define a new Hierarchical Transformation.