Empyrean Propylaeums

Difficulty:  Minimum to survive
Level Restriction:  20+ for Fire and Ice Propylaeums, 50+ for Lightning and Acid Propylaeums
Timer:  30 Days, but the writ rewards are one time only
Can be Solo'd?  No
Rewards:  Bracelets of Frost, Fire, Lightning, and Acid, Writs, and Experience

Gaerlan the rogue Empyrean used 4 Cisterns across Dereth to fuel his Elemental magic.  Delve deep inside the four Propylaeums and take a piece of the Prisms inside.

There are four Propylaeums, located near the remains of the old Essences of Magic.  They are:

Empyrean Ice Propylaeum - 53.2N, 62.5E

Empyrean Fire Propylaeum - 73.5N, 2.6W

Empyrean Acid Propylaeum - 31.6S, 74.2W

Empyrean Lightning Propylaeum - 87.1S, 9.6E

Each dungeon has two rewards - a fragment of the elemental prism and a Bracelet.  Return the prism to an Agent of the Arcanum and you will receive Experience, one or two writs if this is your first time through, and a craftable version of the prism.  Once you have fragments of all four elemental Prisms, you can combine them into a Prismatic Plume, which can be attached to a Niffis Helm.  The result is the Helm of the Elements, which would be very useful against Hollow Elementals (if they existed).