Where should I put a sub-menu on the screen?

Question

This might seem like an odd question, but where should I put a sub-menu on the screen, assuming the main menu is horizontal - similar to the Questions/Tags/Users/Badges menu on this site.

The sub-menu uses just contains actions that pertain to the section they are currently navigating within the web app. Should I put it vertically on the left? On the right? If those are the only two reasonable options, I'm torn between having the menu show up first or wanting to put it off to the side so that the interesting content on the page is seen first.

Should I maybe make another horizontal bar below the main one? Just use buttons or make it part of the layout?

Any other options?

Answer 1

Put the sub-menu below the main menu. The biggest reason is that it gives context to the sub-menu and makes it clear that it is a sub-menu of the menu above it. Putting it pretty much anywhere else doesn't make it clear that it is a sub-menu.

But it also allows you to nest menus if you need it. Take a look at the example from this site, and you can see that it works well. No confusion and even though there are 3 levels of menus, I haven't heard of anyone getting it confused. Just make sure that your sub-menus actually look like sub menus by de-emphasising them relative to the main menu(s).