Astrariums are Tevinter puzzle devices in sets of threes in different Regions. Solving the three puzzles within a location will open up a special vault containing higher tier gear. They allow you to unlock the secrets of the Heavens. Recreate the image of a constellation by connecting the stars without making the same line twice.
"Regarding your inquiry regarding the so-called "Astrariums", it is our considered belief that these are relics from a cult that existed in the pre-Andrastian era of the Tenvinter Imperium. Now, that would be considered a cult in a sociaty that worshipped the Old Gods? An order of magisters who believed in the destruction of the Magisterium, the governing body of the Imperium that determines which mages are and are not given the "Magister" Title.The members of this order wished to return to an earlier period where dreamers ruled, and evidence indicates they operated throughout Tevinter, though primarily in the frontier areas. There they would lock away their secrets, caches of treasure, and perhaps even secret meeting places (thought we have no way of knowing for certain), unlockable only through knowledge of ancient astronomy - a practice that was, we understand, rather out of fashion in the late Tevinter Period.
According to our investigations, each of the Astrariums could point to the secret cache if one knew the three constellations that mapped to each device present a the site. Connect the Dweomers in the correct configuration, and it will be revealed. Many of these relics were sought out by Andrastian cultists in the early Divine age (the Order of Fiery Promise in particular) and destroyed. Why? Because they believed the Astrariums held together the Veil, and destroying them would destroy the Veil and thus the world. Such is the way of cults of any kind that the true reason for what they do could never truly be understood by modern minds.
-- From a letter written by Magister Pelidanus, Head of the Corial ORder, 5:12 Exalted"
Astrariums in The Hinterlands
Three Astrariums can be found out in The Hinterlands. After completing all three you will gain access to a hidden cave located inside the Apostate stronghold. Within a container inside the cave you will find a rare dagger. ( Snake Blade)
Video walkthroughs for solving each of the three Astrarium puzzles out in The Hinterlands can be found here.
Astrariums in the Approach
Three Astrariums can be found out in The Western Approach. After completing all three you will gain access to a hidden cave located just east of Craggy Ridge Camp. Grab some Veilfire on your way in as you'll discover a Fire Rune Schematic etched on the wall in here. You will also find a set of light armor. ( Superior Enchanter Mail).
Video walkthroughs for solving to each of the three Astrarium puzzles out in The Western Approach can be found here.
Astrariums in Crestwood
Three Astrariums can be found out in Crestwood. After completing all three you will gain access to a hidden cave located in a ravine in the Rocky Slope region east of Caer Bronach Keep. Within a container inside the cave you will find a unique belt. ( Superb Belt of Fire Resistance)
Video walkthroughs for solving each of the three Astrarium puzzles out in Crestwood can be found here.
Astrariums in the Coast
Three Astrariums can be found out on The Storm Coast. After completing all three you will gain access to a hidden cave that is tucked into the side of a hill southwest of the southern most Astrarium. (This cave is easy to miss.) Within containers inside the cave you will find a unique bow ( Bane of Red Crossing) and the Free Marches Banner Crown.
Video walkthroughs for solving each of the three Astrarium puzzles out on The Storm Coast can be found here.
Astrariums in the Graves
Three Astrariums can be found out in The Emerald Graves. After completing all three you will gain access to a hidden cave that is located near Argon's Lodge. Within the cave you will find a unique staff ( Deathward) along with a few additional containers that will produce random loot.
Video walkthroughs for solving each of the three Astrarium puzzles out in The Emerald Graves can be found here.
Astrariums in Frostback Basin
Three Astrariums can be found out in Frostback Basin. After completing all three you will gain access to a hidden cave that is located near Cliffside Camp. Within the cave you will find a unique sword ( Hakkon's Honor) and the Masterwork Jagged Battleaxe Schematic.
Video walkthroughs for solving each of the three Astrarium puzzles out in Frostback Basin can be found here.