Destiny 2 features the Legendary Quest Spirit of the 14th Saint. This quest has a total of nine steps which you need to finish to finish the quest.
One of those steps requires that you find the spirit of the saint that is 14th:
An impossible task — Saint-14’s Ghost
The Vex transponders you planted have discovered a network signal in the Cistern at the Pools of Luminance. Head there and see if you can open a gateway into the Vex network.
Saint-14’s Ghost Location
To find the Saint-14’s Ghost you have to travel to the planet Nessus. Land there at the cistern and then go to the gate location.
The path can be a little confusing and difficult to explain, so we’ve included a video below.