This is a fairly common menu structure for Drupal developers to deal with, and depending on how it functions, it could be super easy. Here's the scenario: you need to display the 1st level of links in a menu horizontally, and the 2nd level in that same menu right beneath it.
There are at least two different ways that this can be implemented. The first is a static approach, where you do NOT need to show children of each primary link when hovering.
Consider this menu strucure: