This large and cumbersome apparatus is covered with an assortment of levers, knobs, and buttons, looking remarkably like a cross between a printing press and a giant globe of inter-connecting circles. The artifact is constructed of ancient metals, (mithral, adamantine, bronze, copper, brass) standing approximately 7 feet in height and the same in with/circumference, weighing one quarter of a ton. With it, a character can transport an entire structure, such as a vehicle or a small tower, anywhere on the known Multiverse in a great display of Plane Shift. As its name implies, the Astrolabe of Xonthal was crafted by the most powerful of wizards from the Age of Netheril, and safely stored in the treasure vaults of the Archmage and creator Xonthal in his Maze Tower.
A similar artifact, the Astrolabe of Nimbral, (which was destroyed accidentally by a Halruuan Wizard during the Time of Troubles) was built by Archmages of Nimbral using similar magical blueprints. The main difference between the two is that while one allows for magical teleportation only within the terrestrial plane of Toril, the Xonthal Astrolabe allows for the full effects of a Plane Shift (as per the 7th level Wizard spell of Conjuration) to transport all occupants to any known Plane of Existence, (wherever the Astrolabe is installed).
The Astrolabe of Xonthal allows one who is skilled in its use, (requires a successful Arcana check) to plane shift an object of up to twenty 10-foot cubes in size, as well as everything contained inside that object, anywhere on any of the known Planes of Existence. To properly understand and control the Astrolabe, the user must spend an action to make a DC 30 Arcana/Intelligence check. Failure by 4 or less indicates the destination is off by 5d10×10 miles; failure by 5 or more means the destination is randomly determined.
Objects moved from one location to another are subject to changes in slope, altitude, and stability in the foundation. Thus, it is considered wise to be aloft (such as in a skyship) before operating the Astrolabe.