Las Noches (in Japanese: 虚夜宮, Rasu Nōchesu; Spanish for "The Nights", Japanese for "Hollow Night Palace") is the main base of Sōsuke Aizen and his army of Arrancar, located in Hueco Mundo. The fortress was once the palace of Baraggan Luisenbarn when he was a Vasto Lorde Hollow and God-King of Hueco Mundo. Back then Las Noches had no walls or roof, since Baraggan stated that he was ruler of all of Hueco Mundo and that the sky itself was his roof.
Las Noches is an immense structure that can be seen for miles around and could easily be called the largest structure ever seen in Bleach. Las Noches is so enormous that Ichigo and his friends ran towards it to the point of exhaustion, but did not make any progress getting closer to it, which made Ichigo think it might have been nothing but an illusion. Nel Tu once said that getting from one spot on Las Noches' wall to one of the gates would take 3 days.
The fortress consists of a larger domed building that acts as its center with five towers on top of the dome that seem to hold important places like Aizen's throne room or the Espada's meeting chamber. On the inside, the dome of Las Noches simulates the blue sky of the Soul Society and the Human World, which Aaroniero Arruruerie claims allows Aizen to observe what happens inside. However since he was using this as an excuse to stay out of the light in order to keep using his shape-shifting power, this might be a lie. The halls within Las Noches can have their positions altered, so that a person controlling them can control an intruder's movements. Espada ranked fourth or above are not allowed to release their Zanpakuto inside Las Noches, since the power resulting from that release would destroy the structure. Use of a Gran Ray Cero is also forbidden within the fortress, for that same reason.
There are numerous rooms and areas within Las Noches including
- Medical Facilities - An area where Arrancar can get their injuries healed.
- Espada palaces - The quarters of the Espada, which include Szayel Aporro Granz's lab.
- Tres Cifras - The living area of the Privaron Espada with differently designed areas for each of them.
- Throne Rooms - Aizen's throne rooms, both of which are located in the 5th tower of Las Noches.
- Control Rooms - Rooms where Gin Ichimaru and Kaname Tōsen control the halls of the fortress and monitor the progress of intruders.
- Meeting Hall - The room where the Espada hold their meetings.