Destiny 2's Delve Deeper is the middle section of the Eater of Worlds Raid Lair that's part of Curse of Osiris, following on from Escape the Reactor.
Starting Delve Deeper and avoiding pistons
After dropping down and following some linear passages following the Reactor, will see you in a giant engine room, with pistols firing in the background. When they fire, it'll send a shockwave that'll kill anyone who is out in the open.
In order to safely navigate the giant pipe running to the doorway on the other side, you must wait behind the small, two-sided barriers along the top.
There are plenty of barriers here, and loads of time between pistol fires that moving from one to the end to the other without getting hit should be straightforward. You can probably skip every other barrier, but if in doubt, run from one to the next and take your time.
How to find the Delve Deeper secret loot chest location
Continue going through more passages, until you come to a long, circular tunnel that looks not unlike the start of a James Bond film.
At the end, you and your team will be propelled through distorted, strange space, flying past giant floating rocks. To move past them, wherever you are aiming (or looking at) is the direction you'll fly in.
Gravity obviously plays a part, but it means you can navigate past rocks and safely land on the large land mass at the end.
Before you progress, however, there is a secret chest to activate in this section. As you were flying, you probably saw giant rings. If you fly through each one as a team - the ones you haven't activated are red inside - then you'll activate a chest at the end, usually with a Powerful Gear level engram.
Thankfully you don't have to do this in a single attempt. If you land and you haven't activated them all, then simply jump from the edge (don't let anyone revive you) and you will respawn back at the top of the chute that fires you out.
Looking for more help? When you're not looking forward to Destiny 2's Crimson Days event, our Curse of Osiris guide and walkthrough can explain everything with the recent expansion, including the new Eater of Worlds Raid Lair and how to get Lost Prophecy Forge weapons, new Destiny 2 Exotics and Masterworks weapons and armour. We can also help you reach the 330 / 335 max Power level cap , decide what to spend Glimmer and Legendary Shards on, how Mods, Infusion, and Engrams work, plus a full walkthrough of the Destiny 2 Leviathan Raid.
The rings are dotted around the rocks - the one we struggled to find is at the 'bottom', and seemed easy to miss. This video by Dychronic shows the location of a handful of them if seeing it in motion helps:
Once you are done, take the series of floating rocks towards the next land mass and Break the Barrier, the first phase of the boss encounter.