Threshold

Pour the iron filings out into a line across a doorway, windowsill, or similar portal no more than 10 feet in any dimension. Once you do so, an invisible wall of force springs up to block the entrance. The wall only prevents creatures from passing through and does not impede projectiles, spells, objects, or other attacks. The wall is immune to all damage but can be dispelled if targeted by a Dispel Magic or Disintegrate spell of a level equal to or greater than the level at which you cast this spell.

When you cast this spell, you can designate any number of creatures that can freely pass through the barrier. Any other creature must make a Charisma saving throw when it attempts to cross the barrier. On a failed save, the creature cannot pass through the wall for 10 minutes, after which it can attempt this save again. On a successful save, a creature can pass freely through the barrier for the spell's duration. If you recast the spell in the same position, you can designate new creatures to be allowed through and reset the ability of undesignated creatures to freely pass through.

If you cast this spell in the same place for 30 consecutive days, the effect becomes permanent. As before, a permanent version of this spell can be dispelled by a Dispel Magic or Disintegrate spell of a level equal to or greater than the lowest level you cast this spell for the consecutive 30 days. Similarly, you can change which creatures are permitted through the wall by recasting this spell on a permanent version.