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

Niantic has announced a new event for Pokemon Go. For a limited time, the developer will be hosting Adventure Week, an in-game event that features a variety of bonuses, including extra XP, Candy, and increased Pokemon spawns.

Adventure Week kicks off today, 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.