I have created a custom taxonomy, and that works.

But here is the problem;I have created an archive page, which in the url gets e.g. this: ?category=23. Then, in functions.php, I do this:

function add_inspiration_category( $q ) {
    if (is_post_type_archive(\'inspiration\') && !is_admin()) {

        $category_id = $_GET[\'category\'];
        if (!empty($category_id)) {
            $q->set(\'tax_query\', array(
                array(
                    \'taxonomy\' => \'inspiration-taxonomy\',
                    \'field\' => \'id\',
                    \'terms\' => $category_id
                )
            ));
        }
    }

    return $q;
}
add_filter(\'parse_query\', \'add_inspiration_category\');

So, basically I\'m filtering the archive pages result based on the id in the url. This works, except when I\'m filtering on a category, the main menu dissapears from the header. If I remove the ?category=23 from the url or comment out the section above where I set the tax_query, it works as expected again. Anyone know what this is?