Every once in awhile, Destiny 2 will task you with specific challenges on each planet. One of the challenges you can receive on Titan (my personal favorite planet) is the "kill 40 (sometimes 50) enemies in the New Pacific Arcology." This objective is extremely misleading because, in fact, the entirety of the Titan map is technically the New Pacific Arcology.
Unfortunately, just killing enemies anywhere doesn't count towards the challenge, because there is an unspecified area that Destiny 2 wants you to go to. Thankfully, we've figured it out and are going to help you find the right part of New Pacific Arcology in Destiny 2.
New Pacific Arcology Destiny 2 Location and Challenge Guide
What the New Pacific Arcology Destiny 2 challenge is actually wanting you to do without telling you is go to the Solarium on Titan and kill the enemies there. You can reach the Solarium the fastest by fast traveling to The Rig and going directly east. The Solarium is a private area so, for better or for worse, you won't encounter other random players.
You may remember this underground area from some of the quests and a strike. There are a ton of enemies dueling it out here, so finding the right number of enemies will be a breeze but it is easy to jump right into the middle of the battle and get overwhelmed by the sheer amount of enemies.
The Arboretum and Festering Halls can also be accessed from the Solarium. They, too, contain a lot of potential targets to complete your New Pacific Arcology Destiny 2 challenge with. We recommend taking your approach slowly in this relatively dark area so you can take out the enemies a few at a time, as there are typically some powerful mini-bosses here. Good luck, Guardian!