In the Free Comic Book Day 2008 issue "Pixies and Demons", the X-Men head into the mines of Abergylid chasing demons. On their way down on a lift, Emma Frost telepathically says to Pixie, "I can feel how afraid you are of this place. And why. Do you want me to remove that fear?" Pixie replies, "No, thank you. There's--too much else attached to it."
What is Pixie referring to - what significance do the mines hold?