Near the edge of the Millenium Woods, on the way from First Landing to Millenium Seqouia, in one of the hills an illusory wall can be found. Behind it is a system of caves that leads to the entrance to an ancient temple.
Inside of it, murals show people of all ages, mostly elderly and sick, praying to a humanoid whose heart appears to pour an essence that grants those who drink it life and cure sickness.
Now, this temple is a twisted image of its former glory - the entirety of it is flowing with dark miasma that saps the very life force from living beings, and animates the masses of undead that reside within. Most of those undead are simple fodder, undead who can be destroyed with mere touch of a weapon, but the sheer amount of them makes for a terrifying force.
The wave of those undead made it impossible to explore the temple completely - the only parts that were remembered and recorded are the haunted fountain near the entrance, large hall filled with tombs and dark miasma, hallways filled with entrances to cells, and an altar.
River of pure negative energy that is the miasma, is flowing into the main altar chamber, from where it continues to spread throughout the temple. This river, however, seems to originate elsewhere, but... no living creature could survive following it to its source.