The ending

[Dulgii]

At the end of Legend of Grimrock do your players escape the dungeon before it explodes? If so how? The explosion looked like it destroyed a large area.

[Sol_HSA]

Magic?

[Sir Tawmis]

I kind of address this in my Legend of Grimrock: Destiny's Chance fanfic, by what Coy explains:

"The teleporters scattered throughout these dungeons – like the one that your mage friend passed through – are efforts by the Undying One trying to create a portal that would lead outside of the mountain. The first mages cast a spell around Grimrock that should prevent the Undying One from doing that… but it’s been a long time, their spell is weakening, while the Undying One is growing stronger. It’s only a matter of time before he gets a portal open and out of here. If we can destroy him, and if your mage friend isn’t turned, he could channel the magic released by the Undying One and create a portal out of here.”

[Dephinroth]

I remember that the cube speaks of a portal. Shortly before his awakening.