Hi,
Last year, Caleb ruled that you can still play attachments on locations that are immune to player card effects . If a card cannot have attachments, then it will read "Cannot have attachments." However, cards that are immune to player card effects will be immune to the abilities of attachments. So you can play Power in the Earth on the Troll Cave, but it will have no effect on that location. Card like Ancient Mathom and Path of Need work differently because they don't affect the location, so their abilities will still work.
However, this ruling has changed in FAQ 1.5:
Q: Can I play an attachment on an enemy or location that is immune to player card effects.
A: No. Playing an attachment on a card is a form of targeting, and cards with "immune to player card effects" cannot be targeted by player cards.
I have sent the question to Caleb and will report if the FAQ updated rule is an error or if effectively he has reconsidered his ruling. I liked the original one though.
Edited by zeb