Scattered throughout the Wild Area are Pokemon Dens, where Max Raid Battles against Dynamax and Giganatamax Pokemon take place. Randomly, Pokemon Dens will become active. Some active Pokemon Dens will include a Max Raid Battle, while some will not. If you interact with an active Pokemon Den with no Max Raid Battle occurring, you will receive less Pokemon Watts than if you interact with a Pokemon Den that does.
After interacting with a Pokemon Den and participating in a Max Raid Battle should it have one, the Pokemon Den will become inactive for a given period of time. In order to activate an inactive Pokemon Den, you can use a Wishing Piece to summon a Max Raid Battle. Wishing Pieces can be obtained by staff members within the Wild Area that sell them, and they'll each cost 3,000 Watts. You can also obtain Wishing Pieces from the Digging Duo and as a reward from a Max Raid Battle. There are loads of Pokemon Dens to find in the Wild Area, and each can be home to Max Raid Battle. Each Pokemon Den has specific Possible Raid Boss Pokemon for Max Raid Battles.
We have questions and answers related to this topic which may also help you: