PHP: Get value out of array

Simple probably but can't get it right. I need a value out of an session array here's how its build:

print_r($_SESSION); //gives:

Array
(
    [cart] => cart Object
        (
            [config] => Array()
            [maincurrency:cart:private] => GBP
         )
)

The code so far:

foreach($_SESSION['cart'] as $category => $thing) { 

    echo $category; //echo's config |the value I need GBP
    echo $thing; // echo's Array

if ($category == 'maincurrency:cart:private')
    {
        echo 'found_it'; //doesn't echo
        echo $category; //echo's nothing |the value I need GBP
        echo $thing; // echo's nothing

    }
}

The string I need is 'GBP' from maincurrency:Test:private.