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ADD - Wonderful fully-stocked Chabad shul in the international departures area.
AMS - Further down along the gates there are a bunch of little secluded areas hiding behind shops and restaurant.
BRU - There are 2 Shuls, 1 in each terminal. follow kneeling signs. In the Schengen terminal it is next to the lounges. In the Non-Schengen you go up a floor over the plaza, and its at the far end.
CRL - Charleroi (Brussels South) Airport: at gate 13, take elevator/stairs to - 2 and proceed left where you find many enclaves where you could pray quietly.
FRA - Shul - (may be before or after security ((maybe near gate 96)).
JFK - Shul - T4 second floor all the way to the left only, before security.
KEF - Keflavik, Iceland: After customs, make a left right before the BSI ticket counter and go down the stairs. Make another left and you'll find a great, quiet space mostly hidden from view by the staircase.
MDW - still have old phone booths where you sit away from the crowds
TLV - 2 Shuls - one after security next to the Beit Chabad. One one flight up from the arrivals hall.