It's a random spawn crypt during the quest "Shattered Crown" in Act 1. Im not sure if it spawns on Normal mode, but i have heard it only spawns randomly between Nightmare and Inferno. All the mobs inside it are named after the artists/designers/technicals.. basically all the developers of D3.
Here, have a look:
As you can see in the last photo, the boss of Development Hell is Lead Designer Jay Wilson. After killing him, you receive an achievement called "Smash, Jay Smash!"
![casivo](https://swtorstrategies.com/wp-content/uploads/2023/10/Casivo-Logo-6.png"){kind=logo}
