But even if you're not at the Pokemon GO Fest, you can still join the festivities and catch Pokemon during the Challenge Windows.
Niantic says Pokemon Go has been downloaded 750 million times.
Some Pokemon Go fans traveled from other countries to attend the event.
Niantic said it will refund the $20 ticket price and players or Pokemon "trainers" would be given $100 in PokeCoins for their Pokémon GO account.
While many attendees blamed internal app glitches some also blamed poor internet connectivity and phone carrier service.
Despite a (very) rough start, it seems that Pokemon Go Fest has accomplished what we hoped it would, and unlocked Legendary Pokemon in Pokemon Go.
"Almost everyone on the festival grounds who didn't have Sprint as a provider was unable to log in to the game", said Brandon Omernik, 23, in a discussion with CNN.
The issues were so severe that Niantic CEO John Hanke was heckled loudly when he took the stage this afternoon, with angry fans shouting and chanting "We can't play!", "Fix the game!", and "Fix the servers!" While Pokemon Go was great publicity for the Pokemon franchise last summer, we can't help but wonder whether the franchise is now getting negatively impacted by Pokemon Go's constant bad press. However, Niantic is doing everything they can to try and right the wrongs, they released an update on their website letting everyone know what to expect.
Legendary Pokemon Eggs will have a small chance of appearing in Pokemon gyms and when players defeat a legendary raid boss, they will have a small chance of catching a legendary Pokemon.
"Pokemon GO" Fest participants will get the chance to get legendary monsters before they are launched in-game worldwide.