XI is located in the south west of the map, south of Meridian. Unlike the other Cauldrons, your primary enemy here will be the Cultist human enemies rather than Machines. Climb up to the entrance where you’ll come across a dig site for the Cultists. There’re no corrupted Machines here, so it’s just you and human enemies, and there’s only 1 elite as well, so you shouldn’t have much trouble defeating them. Once you have, search the bodies for a key to the rest of the Cauldron.
Once inside, follow the tunnel down. You’ll come across a couple of patrolling Cultists, kill them then keep going until you reach a section where it widens out. There are a few more patrolling Cultists here, as well as a few Blaze canisters that you can detonate as a trap.
Once they’re all dead, keep going until you reach an expansive cave. Rappel down to the ground then make your way through the area towards your waypoint marker. There are a good number of Cultists in here, along with a few Elites, so avoiding direct conflict is a decent plan. Keep using your Focus to scan around as there are a lot of supply crates dotted about the place, including on top of the two derelict Tallnecks. Either kill or sneak your way through the area to your waypoint marker.
Once you reach it, keep following the route through the caves. You’ll reach a natural cave with medicinal mushrooms, if you need healing items definitely stock up then keep going. Eventually you’ll reach the Cauldron Core. This area is patrolled by a couple of Deathbringer gun wielding heavies and a bunch of other Cultists. Luckily there are also a lot of blaze canisters scattered around, as well as a good deal of cover. Use the edges of the area to skirt around behind the bad guys and get the drop on them.
When the room’s cleared, override the Core. Unfortunately this will also attract a bunch of Cultists and you’ll have to defend the Core against them for a set time. Best bet is to grab a Deathbringer gun and let rip on them as they come through. After a short while though, Machines, summoned by the Cauldron, will arrive and start attacking the Cultists as well. The best way to handle this is to override a couple of them, especially something like a Ravager, and just watch the chaos happen.
Once the timer’s done, you need to find a way out of the Core. Head up this ramp here:
Hop across the machinery then climb up the various scaffolds out of the room. Follow the tunnel through until you drop out of the tunnel into a room where two Cultists will immediately get attacked by a Stalker. Either avoid or kill the Stalker to move on. With Stalkers, hit them with Tearblast to get rid of the stealth and the forward gun, then use a Ropecaster to haul them down for a critical strike or two and you’ll beat them in no time.
Once it’s down, head to the back of the room on the ground flood to find an overrideable door. Go through that and you’ll end up back in the big cave with the Tallneck derelicts, only this time there are Cultists and Machines. Now you can fight if you want, but unless you’re desperate for parts or shards, there’s not any real point. Head through the area and climb the pylon and the use the handholds to climb up into the tunnel. A group of Cultists and Machines will be battling it out here, again, it’s your choice as to whether you want to fight or not. Either way, keep following the path upwards towards the entrance again, avoiding or killing Cultists who are in your way. When you get to the entrance, you’ll find the Cultists doing battle with a bunch of Machines. Use the zip line to rope right over the top of them and that’s Cauldron XI complete.