If you're looking for the Destiny 2 Sanctum of Bones Lost Sector then chances are you're on the Exodus Evacuation quest for the Traveler's Chosen Exotic sidearm. It's a fairly straightforward task for the most part - like the prequel quest released earlier this season (which you've likely unwittingly completed), it tells you to visit Io, Titan, Mercury, and Mars and complete some basic tasks like Strikes and Lost Sectors. The quest is relatively short and mostly self-explanatory, but there are a few sections that are easy to get hung up on, so we've prepared a short guide explaining these and how to clear them easily.
Destiny 2 Sanctum of Bones location
The Io portion of the Exodus Evacuation quest will tell you to clear the Sanctum of Bones, which is a Lost Sector located near Asher Mir. The tooltip actually says this, but if you aren't familiar with the planet's Lost Sectors (and who is, really?), it's easy to overlook it.
The Sanctum of Bones Lost Sector is located directly across from Asher Mir. You genuinely just need to stop talking to Asher, turn around, and walk forward. Here's what the entrance to the Lost Sector looks like:
Just scuttle inside and continue your quest.
Destiny 2 Methane Flush location
This is a similar situation, just on Titan. You'll need to clear the Methane Flush Lost Sector to proceed, and again, it's easy to miss. Fortunately, this one's even easier to find. You can see the entrance to Methane Flush from the Siren's Watch landing zone:
Once again, head on down and clear out the baddies to progress.
Destiny 2 Festering Halls location
The last sticking point is a bit trickier, as it involves exploring in patrol mode rather than entering an instanced activity. The Titan portion of Exodus Evacuation tells you to clear out special enemies in the Solarium and Festering Halls, which are located on the right side of Titan past the Rig (per the map above).
To get there, set down at the eastern landing zone and head east until you reach this doorway:
Follow the linear path forward (taking the same path as the Siren's Song Strike) until you reach this room. You'll find the first special enemy here:
Next, take a right (the opposite path as Siren's Song) and continue until you reach this room in the Festering Halls. There's an enemy here as well:
Finally, keep moving forward, jumping down an orange-lit shaft along the way, until you reach this chamber. The final enemy is located here: