What does the cryptic crossword clue "Where a flyer may go for a walk in London? (8)" mean?

The definition is "Where a flyer may go". The wordplay uses a charade (building blocks). Double definition The answer is BIRDCAGE.

Where a flyer may go for a walk in London? (8)

Times Cryptic #27883 | 17 Down | 2021-01-25 flower