Removed link, problem solved
The menu at the top is supposed to be a dropdown menu, but it expands to the right instead.
My CSS is this (I believe this is the relevant bit anyway)
#primary-nav, #primary-nav ul { list-style: none; margin: 0px; padding: 0px; }
#primary-nav ul { position: absolute; top: auto; display: none; }
#primary-nav ul ul { left: 100%; top: 0px; }
#primary-nav li { float: left; }
#primary-nav li li { float: none; position: relative; }
#primary-nav ul, #primary-nav li:hover ul, #primary-nav li:hover ul ul,
#primary-nav li.menuparenth ul, #primary-nav li.menuparenth ul ul { display: none; }
#primary-nav li:hover ul, #primary-nav ul li:hover ul, #primary-nav ul ul li:hover ul,
#primary-nav li.menuparenth ul, #primary-nav ul li.menuparenth ul,
#primary-nav ul ul li.menuparenth ul { display: block; }
I have no clue where exactly the direction for the menu is set.