The Lighthouse is a new social space on Mercury.
This is the hub section for Mercury, it has numerous mysteries inside it and will lead to many more across Mercury.
It is here you will encounter Brother Vance. There are numerous disciples of Osiris found in the area.
There is also a large wall glyph on one side. This will function as a tracker of your end game progress within this DLC. It will allow you to see what you have done and what is left for you to do. These glyphs are tied to optional quests that you can complete and then use the items earned with the Forge to create weapons that have been adapted to Vex Technology.