Benefit

You can attempt to cast a spell against targets that are sheltered behind a wall or force effect. Your spell briefly skips through the Astral Plane to bypass the barrier.

The strength and thickness of the barrier determine your chance of success. To successfully bypass the barrier with your spell, you make a Spellcraft check against a DC equal to 10 + the hardness of the barrier + 1 per foot of thickness (minimum 1). Assign a hardness of 20 to barriers without a hardness rating, such as force effects (or a wall of ectoplasm). Force walls or walls of ectoplasm are assumed to have less than 1 foot of thickness unless noted otherwise.

If a spell requires line of sight (which includes most spells that affect a target or targets instead of an area), you cannot cast it as a burrowing spell unless you can somehow see the target, such as with clairvoyance.

A burrowing spell uses up a spell slot two levels higher than the spell’s actual level.