Example of page route in Drupal, with the Cool module

MyPage.php

<?php

namespace Drupal\my_page\PageControllers;

class MyPage implements \Drupal\cool\Controllers\PageController {

  public static function accessCallback() {
    return TRUE;
  }

  public static function getDefinition() {
    return array(
      'title' => t('My page')
    );
  }

  public static function getPath() {
    return 'my-page-url';
  }

  public static function pageCallback() {
    return '<h1>' . t('This is my new page!') . '</h1>';
  }

}
?>