wp_title() shows 404 – installation outside WP

You could do an outside query instead.

<?php
define('WP_USE_THEMES', false);
global $wpdb;
require(ROOT_DIR.'/blog/wp-load.php');
query_posts('showposts=1');

get_header();

try{
    $args = array('post_type' => array('post'), 'posts_per_page' => -1);
    $qry = null;
    $qry = new WP_Query($args);
    if($qry->have_posts()){
        while($qry->have_posts()){
            $qry->the_post();
            $theTitle = get_the_title();
            print $theTitle.'<br>';
        }
        wp_reset_query();
    }else{
        print 'no records found';
    }
}catch(Exception $e){
    print $e->getMessage();
}

get_footer();
?>