Shin Megami Tensei: Persona 4

How do I get past Adachis lvl?

After the 2nd mini boss were do you go?

Go back to the ominous bedroom and proceed into the dungeon, instead of going to the 6th floor of Magatsu Mandala, choose to go back to Magatsu Inaba's 1st Floor. Proceed down to the 2nd Floor and there will be a sealed door at the north part of the map which can now be unlocked. The next floor is the floor with the boss