Loadstone of the Planes
This arrow-shaped piece of magnetite bound in electrum whirls in the air, directing you to a portal you're looking for.
Wondrous Item 3,400 gp
Special. Use this power during a short or an extended rest only. You learn the direction and rough distance to the nearest portal connected to a plane of your choice.
Published in Manual of the Planes, page(s) 158.