Mirrorstone

Mirrorstone is a curious phenomenon found almost exclusively underground, or in dungeon environments. Space ends up folding a bit in chambers with mirrorstone, and most chambers have multiple patches of mirrorstone on walls, ceilings, or floors. When one stands on top of a patch of mirrorstone, one is capable of seeing to other patches of mirrorstone and even casting spells or similar effects through it to hit someone else standing close to another patch.

Mirrorstone

Seven Kingdoms: Seowyn's Crossing aethan