Haider of Sweden wrote:If I enter the URL manually, I still get to the location where the menu led to previously.
Is there any way to redirect people entering the URL or is it inevitable that the sub-directory will be there?
It's always going to be a page, regardless of what settings you apply for it in the menu. If nobody can access it via navigation, is it strictly necessary to attempt to disable the page itself? Worst case scenario, someone will find a page which contains links to the subfolders as specified in the menu.
If you want, you can set a redirect link from page settings > link:

Just link to another page, for example the home page "/", or "/another/page/".