Forbidden Hoard
The Forbidden Hoard spawns at various locations around the Forbidden Reach. The chest contains a 
[Zskera Vault Key], roughly 500 
[Elemental Overflow], and occasionally a Primalist loot token, an 
[Untapped Forbidden Knowledge], or 
[Cliffside Wylderdrake: Coiled Horns].
While on 
[70] Plunder Siege, 
[Atrenosh's Journal] can be found inside.
Opening ten hoards is the objective of 
[Forbidden Spoils], itself a criterion of 
[You Know How to Reach Me].
Locations
Atop a tower in Caldera of the Menders at [36.0, 34.0] south of the Support Creche guarded by a Territorial Proto-Drake.
In a small unnamed cave northeastern of Caldera of the Menders at [44.6, 32.5] guarded by two Scythid Aggressors.
Inside the Earth-Warder's Cauldron at [40.9, 69.0] [45.4, 76.1] of the upper War Creche beneath the Old Weyrn Grounds guarded by three Spellsworn Guards.
Inside the broken tower of Lost Atheneum at [55.0, 34.7] on the high floor, guarded by three Tarasek Plunderers.
Inside the Lost Grotto of Caldera of the Menders at [49.2, 37.2] guarded by two Scythid Aggressors.
On the western Frosted Spine at [46.5, 74.8] in a small cave guarded by a Territorial Proto-Drake.
On the eastern Frosted Spine at [53.3, 78.1] on a remote plateau guarded by a Territorial Proto-Drake.
East of the Froststone Vault at [62.9, 44.1] at the spring that feeds the river guarded by three Tarasek Plunderers.
North of the Lost Atheneum at [57.1, 22.7] in a small unnamed cave guarded by fungarians.
East of the Old Weyrn Grounds at [56.1, 56.3] on a small island in the river guarded by two Spellsworn Guards.
Northeast of the Old Weyrn Grounds at [62.7, 49.3] across the river in a small cave guarded by three Tarasek Plunderers.
On the southwest Shrouded Coast at [39.3, 24.3] inside a tower near the pass to the Caldera of the Menders guarded by four Irontide Freebooters.
On the northeast Shrouded Coast at [46.0, 16.3] at sea level by the vrykul shipwreck guarded by two skeletal Drowned Pillagers.
At Skyward Watch at [40.9, 11.2] inside a tower off the northwestern shore of the Forbidden Reach guarded by five Refti Confiscators.
South of the Stormsunder Crater at [69.9, 77.6] on a small island guarded by two Farscale Raiders.
In the Tempest Cove at [29.1, 41.9] on a small island guarded by four Irontide Swoopers.
Patch changes
Hotfix (2024-03-26): A Forbidden Hoard that was inadvertently inaccessible due to having fallen through the floor has been moved to an accessible spot. - Patch 10.0.7 (2023-03-21): Added.