Impulse will automatically create a multi-column "mega-menu" dropdown for your navigation wherever your navigation includes three levels of links.
Each third level of navigation will get split into its own column of links. For example, the layout above was created by the menu below:
To add some visual impact, any second level of navigation that links to a collection with an image will have that image shown above the title of the link. You can see this for Tops, Tunics, Dresses, and Sweatshirts in the example above.