Possible Clues:

• Bird enclosure principally approached by public transport
• Place for fliers
• Zoo building with wings?
• In a German zoo, this kind of building is a Voliere
• In the middle of cave, friars hurrying to build bird shelter
• Big bird enclosure
• Birdhouse at the zoo
• Huge birdhouse
• This place is certainly for the birds
• Its inhabitants probably like flying ace passing through railway