https://www.gamespot.com/articles/new-pokemon-go-adventure-week-event-now-live/1100-6459174/

A new event is now underway in Pokemon Go. For a limited time, Niantic is hosting Adventure Week, an in-game event that features a variety of bonuses, including extra XP, Candy, and increased Pokemon spawns.

Adventure Week kicked off on May 24 at 1 PM PT / 4 PM ET. Among other things, Niantic says the event will feature "unique" Field Research quests to take on, which will offer "exciting rewards." The developer didn't specify what these rewards will be, but it did mention a possible Raid Battle encounter with Aerodactyl.