cat archive general idea

<?php
//# getting the main category of the page
$catid = get_query_var('cat');
$cat = get_category( $catid );

//#check if this is top-level cat//
if( !$cat->parent ) : //there is no parent cat, therefore this is the top cat//

//# now letz get the children categories of the main category
$categories = get_categories('child_of='.intval($catid));

foreach ($categories as $category) {
    //# check if it is a real parent category with subcategories
    if ($category->parent == $catid):
        echo
        '
        <div class="cat-item">
        <div class="image">'.get_cat_icon("echo=false&cat=".$category->cat_ID).'</div>
        <div class="text">
        <a href="'.get_category_link($category->term_id ).'">'.$category->cat_name.'</a>
        </div></div>
        '

        ;
        //# here we go, getting the subcategories
        $subcategories=  get_categories('child_of='.intval($category->cat_ID));
        foreach ($subcategories as $subcategory) {
            echo '<span class="subcategory" style="padding-left:12px">';
            echo '<a href="">'.$subcategory->cat_name.'</a></span>';
        }

    else : //#not the top cat//

//insert the (normal) loop to output the category posts if the cat is not top level//

    endif;
}

?>