The Coney Island Mermaid Parade kicks off the summer on the first Saturday after the solstice every year. This year it's on Saturday, June 23rd. The parade steps off at 2pm and the Mermaid Ball starts at 6pm. The parade route is from Astroland to W. 16th street along the boardwalk, and then down Surf Avenue between West 16th Street back to Astroland.
If you've never been, it's quite a site: think "art parade + burlesque show + pagan rite of spring + amusement park" and you'll be close.
This is me at last year's parade with a parade regular, his parrot and his poodle.

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