The I.D.P.D. Headquarters is a loop-exclusive secret area. It consists of three full stages, the first two being standard enemy stages and the third being a spacious boss stage. In the first two stages, the only enemies which spawn are I.D.P.D. troops, as well as I.D.P.D. Vans and Elite I.D.P.D.. Since the area is entirely I.D.P.D., no Rads are dropped (unless the player is using Melting). The third stage is home only to the Captain, a secret boss whose difficulty is comparable to that of the Nuclear Throne. Beating the Captain will end your run.
How to enter the I.D.P.D. HQ
It is possible to leave I.D.P.D. HQ the same method done by entering it, as vans still spawn within HQ. This will bring the player to the following area from where they left from, unless if the level is a X-3 level, in which case they will have to redo that level. HQ can only ever be visited once per. run, as trying to re-enter this area will cause vans to explode on the player instead.
- Rich vegetation and clean white color of this area symbolize that it's not affected by the apocalypse.
- There's a diamond symbol that repeats itself on the walls, the I.D.P.D. Vans, the Captain's forehead, desk and on the floor of her office. A similar symbol can be seen in the Palace and on the Throne itself, it also resembles the Proto Statues. What the symbol means and how are all these things connected is yet a mystery.
- The I.D.P.D. Headquarters' theme is "Beyond The Portal".
- If Rogue enters the I.D.P.D. Headquarters, a music track will play unique only for her. It's a piano version of the I.D.P.D. Headquarters theme. The song is titled "The Place I Once Called Home".