Tracking down lost ghost locations in Destiny 2's The Final Shape expansion might not seem like the highest priority when the Witness is set to rewrite all of creation, but doing so will complete the Spirit Guide seasonal triumph, plus get you some coveted red-border destination weapons for the trouble.
You won't unlock these mini-quests until you finish the main campaign and start the Ergo Sum exotic quest that appears immediately after. You can also only recover one ghost at a time, so you won't be able to do that seasonal challenge straight away. Still, these quests do give out a lot of red border destination weapons, and doing the initial missions will unlock the exotic weapon quest Convalescence: Budding, which gets you the kinetic heavy trace rifle, Microcosm.
Convalescence: Rootbound lost ghost location
You'll first unlock the ability to track lost ghosts after you complete The Final Shape campaign and the first mission of the Ergo Sum exotic quest, Queens 1. After that mission, you'll transmat in front of Micah-10's Lost Ghost Analytics. Interact with the console to begin the Convalescence questline.
The first quest, Convalescence: Rootbound, sees you tracking a lost ghost to The Forgotten Deep lost sector. You will have been here during the campaign, but if you can't remember how to get there, use the icon on the map indicating the search area—simply activate this and follow the nav markers to find the entrance.
Fight through the lost sector to the final room and then look for the darkly-glowing ghost in between the massive tree and the platform with the well of bright green light. Interact with the ghost and bring it back to the Arbor of Light—just next to Micah's Conduit—and get your reward of a red-border weapon from Micah. You're not done yet, though; now you've got to heal that ghost.
The Convalescence questline requires you to do a whole lot of other stuff, including getting Flickering Blessings by opening chests, and playing some of the new Overthrow event. After that, you'll have to follow a spirit bird through The Refraction area until you reach your first cyst, Sword Dance. This tiny dungeon is quite simple—you just run through hacking away with a hive sword, smashing crystals and enemies alike. Once you complete it you'll be able to heal that ghost and return it to the Arbor of Light for real.
After that first ghost is returned and healed, you can pick up the Alone in the Dark quest from Micah-10 and start the same process for the next ghost, locating it in a lost sector, completing Overthrow, and finishing a cyst to heal it. You can also grab The Return, The Hellmouth, or The Shadows quests from Micah, which see you looking for lost ghosts in activities in the Cosmodrome, on the Moon, and in the EDZ respectively.
