Head through the Ishtar Commons into the N/Gen Branch. Head down the left side and start clearing out the Fallen. You’ll need to take out a Servitor here; it’s Major level and once destroyed two more will spawn, one on each side of the room. Head back to the entrance at this point so you can battle the Vandals from distance and take out the Shanks before they get too close. Watch out for the Captain that comes with the Major Servitor in the back as it often comes right down the middle of the area looking to wreak havoc.
Take to the second floor and head inside towards Dig Site 4. Clear out the Vex and Fallen here, most of them are fairly weak. Don’t stand too close to the entrance though as Vex will spawn here and could lead to a surprise defeat if you aren’t careful. The hardest part about this open area is the Hobgoblins that will snipe and the Minotaurs that rush you. Use a Fusion Rifle on the Minotaurs and a Sniper Rifle for the Hobgoblins.
Ahead you’ll move through a cave and a large pack of Goblins will attack your position. It’s very easy to mow them down or just use a Super Ability to wipe them all out. This makes this area very attractive for farming Engrams. If you want to repeatedly do this area, move up to the ledge before the drop down into the Nexus to receive a checkpoint then head back and die by leaping into the abyss. This places you just before the large pack of Goblins that can be killed again. Jump off the ledge to reset and continue until you have all the Engrams you want.
When you are ready leap down and clear out the area. There are Minotaurs so be mindful of that. The upper and lower areas are key for cover and avoiding the additional Vex that will join the fight midway. When Sekrion emerges you’ll want to spread out so you aren’t getting hit with the cannons. They do a lot of damage and could easily wipe the entire Fireteam if you are all grouped up. Hit the glowing yellow eye for Precision damage and try to keep your Super Ability and Grenade available for the additional Vex. They spawn at random and in very large waves on both sides of the room. It might take awhile, but the Ultra Hydra will eventually fall.