Open default.php from your theme in a text editor.

Look for the following PHP block:

<?php
$b = new Area('Main');
$b->display($c);
?>

Before the closing PHP tags ?>, insert a few more lines so it looks like the following:

<?php
$b = new Area('Main');
$b->display($c);
echo '<xmp>';
print_r(get_defined_constants(true));
echo '</xmp>';
?>

Open a page of a type without a page template. Remember, we've created a template for the left- and right-sidebars. Pick full width for example, otherwise the inserted code won't be executed.

The output will contain a huge list of constants categorized by modules. At the end there's a category named user; these are the constants which are not coming from PHP itself but rather from concrete5. Look at them and you'll find a lot of constants related to directories and URLs. They might be useful one day.