Whereas my vote would be for an exploration of the Citadels of the gods. It would produce a number of key places that people really should know about (for the ones that can be harmlessly visited) and tons of dungeon delve material for all the citadels that are less benign. Considering what the Citadel of Silence was, that was a show stopper previously, but now that that has been...resolved, maybe the rest of the citadels could be explored more thoroughly.

The Keys of Man and exploring the Citadels of the Gods could be related.

A subplot of a full Pilgrimage to the First City.

I'm pretty sure the Destroyer has already pocketed most of the Keys of Man by this time. See the prophesies... but at least the one from the BI at Origins should still be in play. Assuming anyone can get it out from where it is stuck.

Ah, the Key of Nier. We have plenty of Ardakene and val'Ishi, not no mention Clerics. If Leonydas dies during the procedure to retrieve it, we can just resurrect him.

You may want to reread the 5e spell lists in the Campaign setting.... What is this resurrect thing of which you speak? There is raise dead, but that is much more limited since it has to be done before the next dawn after your death (When your soul would leave your body).

Yes, thank you for pointing that out, I meant Raise Dead. But it's semantics at this point, I don't think he will be dying anytime soon.