A Dying Planet

After you saved Kiiran Dals' team from Remnant Stasis, she mentioned that Havarl was in decline. Though Havarl appears to be thriving, not everything is as it seems.

Acquisition
This mission is automatically received after completing Helping Havarl's Scientists.

Talk to Kiiran Dals about Havarl's problems
Kiiran Dals says that Havarl is having issues: uncontrolled mutations in the wildlife mean that the ecosystem is crumbling away. This appears to be an issue of having only two working monoliths. Torvar, one of the researchers, suggests asking the sages at Mithrava. Kiiran Dals scoffs at the idea, explaining how the sages are hermits that believe in isolating themselves from modern thought.

Find the entrance to Mithrava, the sanctuary
Regardless, you will need to go to Mithrava. Head to the southernmost part of the ravine to find a Remnant door. Once through, continue all the way to the back of the room to find a Remnant console; it will appear out of the ground on your approach. Interface with it to open a nearby wall.

Reach the top of Mithrava
Through the wall is a short corridor, at the end of which a pillar rises. Climb the pillar and head up through the hole. Use the gravity well to cross to Mithrava Ascent, evidently a tall Remnant tower. Use another gravity well to head up; once you land, go out the door.

The path forward is to the left of the exit; drop down from the ledge. It appears to lead to a dead end, but interacting with a Remnant console brings down a platform. Use the pillars on either side to reach it, then jump from the platform to the pillars across the way. Continuing on will lead you to another Remnant console; using it will activate a bridge for you to cross. There are a few Remnant on the other side, so be mindful of the edge while fighting.

At the end of this ledge is a short pillar for you to jump on to reach the next level. Keep moving until you see yet another pillar and climb it to reach a Remnant console. Interfacing with it activates another bridge. Cross it and climb up a few consecutive pillars and ledges to reach a Remnant door, which opens to another gravity well that takes you upwards and finally to Mithrava itself.

First Sage Esmus comes to ask how and why Ryder is here. However, once informed, he says that restoring Havarl is impossible, because they do not have the knowledge of the third monolith or the vault. It is explained that angara believe in reincarnation, and that sometimes memories of a soul can be remembered via familiar items. Zorai, an ancient champion of the angara, was said to have knowledge of the Remnant; however, the soul has been reborn in Taavos, a member of the Roekaar. Esmus gives Ryder the location of an item that belonged to Zorai.