Hall of Termination in is an area high in the castle that, as the name suggests, (seems to be) where Bloodstained: Ritual of the Night comes to an end.
Below, we’ve included a complete map of Hall of Termination with a few notes about the area.
Hall of Termination map
There are two hidden rooms in Hall of Termination. The one in the middle of the area has Gauge Glasses inside — glasses that show you how much health an enemy has remaining every time you hit them.
Once you get (at least) Double Jump from Andrealphus in Livre Ex Machina, you’ll be able to reach the hidden room in the top left. This room has three chests — a Gram greatsword, Celeste’s Key (to reach an optional room in Livre Ex Machina), and some cash — along with a Max HP UP and a Max MP Up.
On the far left of the room, jump and attack the wall to reveal another hidden room. This one contains a portal to a fun secret area that is only one room followed by an optional boss fight.
There is an area under a staircase here with a Max Ammo Up and some bookcases. You will not be able to reach them until you get the Dimension Shift Shard ability near the end of the game.
The main purpose of this area is in the top right. This is where you’ll find Gebel. You can reach this area relatively early in the game, but if you choose to fight him now, you won’t get the true ending of the game.
Instead, wait until you face Zangetsu in the Oriental Sorcery Lab and receive the Zangetsuto. If you defeat Gebel after that point, you’ll get the second ending, but still not the true one. Instead, about halfway through the fight, watch for the moon in the background to turn red, then attack it. This will move you toward the true ending.