Darkest of the outposts created by the Empire during the Empire-Avernum War was the fortress of Angierach. It was built in a remote northern corner of the Unsettled Lands as a place for the Twelve to exercise foul and twisted magic against Avernum.
No other troops were stationed at Angierach; its dark magic so permeated the location that priests who came near it were struck by splitting headaches. Exactly what magic the Twelve practiced there is unknown, but we do know several of their deeds. Avernite prisoners were taken there, and were magically drained, experimented on, and sometimes left to die of starvation. The Crystal Soul Vyvnas-Bok was taken there and tormented. Finally, the rakshasi there experimented with an augmented magic barrier developed by Garzahd.