Bayonetta 3 is finally out and players can now reunite with their favorite Umbran Witch. A new feature added to Bayonetta 3 are Bewitchments which act somewhat like little achievements players can get during their gameplay.
To open up the secret room, you will need to use a summon to break open the path at the poison area in the underground temple. Check on the guide below for more details!
Chapter 8 Secret Room (Bewitchment Guide)

The Secret Room in Chapter 8 can be found in the large room with the poison pool at the center. This room is a puzzle where you have to use a new demon summon named Baal.

Upon entering the room, you can look to your right to see large statues adorning the walls. You will have to use a summon to attack the first statue to your right.
Doing so will create an opening at the top that you can enter. Use your spider form to climb up there and reach the new entrance.

Entering the room will award you the Bewitchment!
At the moment, Bewitchments don’t unlock anything or have any value. Some of them are easy and can be done on the first try, while others will require the player to repeat the chapter to get them. Most likely, Bewitchments are mostly fun challenges for players and for bragging rights.