Wall of Vapors

The Wall of Vapors is the name of the keep belonging to the archmage Katalii. It lies hidden in the ethereal plane.

It looks like a giant wall of smoke extending in both directions which is constantly flowing like a waterfall with frequent flashes of purple lightning.

The Wall of Vapors can only be located through magical means. Once on the ethereal plane, it requires casting a spell of Katalii's own creation (4th level Conjuration, wizard, sorcerer, warlock, bard). Scrolls of this spell are known to exist.