I've removed uploader's description from the artist commentary section:
This is the palace of demons (which is what Pandemonium means literally). After falling into Hell with the rest of the angels, Lucifer decides he'd rather reign in Hell than serve in Heaven, and subsequently builds this palace with the other 100 thousand thousand fallen angels. Once it's built, they go inside and Satan gives a speech, which is when this piece by Martin happens.
I don't think this is artist commentary, especially that it refers the artist in 3rd person.
