By Batman's cape, link below worked before. This link sez Batcave Opens for display on Batman's birthday with all kinds of Batgoodies, for a limited Battime in a Batcave near you.
Sorry, just could not resist for Batman, for me and many of my age, meant not seven and counting versions of movies of uneven quality--c'mon, "Batman and Robin," bit the Bat One. I spoke the obvious line before Dick "Twerp" Grayson said it, "Holy hockey players from hell, Batman."--but meant the 60's TV show, cool for boys in that era.
Now, it still is kewl, but as an adult of this era, might call it camp.
Watch an old episode or three; revel in the simplicity of a bygone era. Kapow indeed!
Plus the show had a great run of guest stars as guest villians; for me, Frank Gorshin will ever be the best Riddler. Keep your Jim Carrey; in fact, the latter's version blows Batchunks.
Evidently, comic book Batman has a few dates we can ascribe for his birthday. This allows me to celebrate them all.