Originally Posted by KARFA

So depending exactly what time of day you are there it's likely the galleries club (for J) and galleries first will be open. If you were just departing in J to ATH you would have access to the GC only.

Since you have arrived in F you will have access to the GF. Go to the GF entrance and show your inbound F bp as well as your outbound J bp.

If your F was on AA that's where you stop. If your F was on BA you can go over to the Concorde terrace which is accessed from the GF and show them your inbound BA F bp as well as the ATH bp to get access.