You can register your own routes in routes.php file within bootstrapDirectory (default is app/admin/routes.php).

Route::get('my-url', function ()
{
    $content = 'my page content';
    return Admin::view($content, 'My Page Title');
});

Route::post('category/my-url', '\App\Http\Controllers\MyController@postMyUrl');
Route::any('my-page', [
    'as' => 'admin.my-page',
    'uses' => '\App\Http\Controllers\MyPageController@myPage',
]);

All routes will be registered with admin prefix and filter.

Important: If you want to render page content within admin interface use Admin::view($content, $title) method.