The Second-Floor is a parallel universe used by the Order to trap members of the PAAB during the invasion of DC during the Second-Semester War. The point of diversion was unknown, but likely something minor as what was shown of the universe was not much different than The Base.
The history of the Second-Floor universe is presumed to be generally the same, as no major differences are noted by the trapped PAAB members.
However, it should be noted the only areas shown were DC and Maryland and not Ethel or Mississippi at all.
When the PAAB members were trapped, the recently-deceased Mr. Rodgers of the Base was swapped with the Mr. Rodgers of the Second-Floor. The trapped members of the PAAB were Chloe, Matt, Mallory (later revealed to be working with the Order), and PAAB-ally Mrs. Musselwhite.
Trapped, the group attempted nonstop to escape the world. They explored Maryland and DC for answers, but they were unable to find any. When The Order/FBI used the Hyperion Cube, it forced Matt, Chloe, Ms. Musselwhite, and Mallory back into The Base.
After the removal, life in the Second-Floor continued as it had done so.
The entrance to this universe is the elevator of the Gaithersburg Hotel. When inside, PAAB-members Matt and Chloe desperately tried to reach the second floor of the hotel and stop the Order from making their swap, but were shocked when the number panel only had the options of '1' and '3', skipping '2'. Mallory led the two, along with Mrs. Musselwhite, to the second floor on foot, secretly trapping them in the universe until the Hyperion Cube was used.