After venturing through the Old Olney Underground, you find the Old Olney S. Wilson Building. It appears to have been an Enclave base of operations, but suffered a major cave-in. Even some Enclave soldiers are still present in the building. There is very little of not on the ground floor, so one should keep to the collapsed second floor if they want to get anywhere. Toward the back, there is a Galaxy News Radio advertisement. It creates a bridge to the third floor which grants access to a hallway that leads to the Olney Powerworks.
Two rare police hats can be found here. One is in an office near a cash register, and another is in the center of the room perched above the toilet on a piece of concrete jutting out from a supporting column. Standing on the empty deathclaw cage enables access to the latter one.
A rare bubblegum can be found on the very bottom floor in the southeast corner.
Two mini nukes, sitting on a ledge inside of the fallen length of radio tower in the center of the area. To retrieve them, you can either shoot them off the ledge and then gather them from the floor below; or make your way up to the east side of the highest level of the building and jump into the length of tower's open end.
It is possible to get to the upper levels by climbing the rubble that is immediately to the left as you enter the open zone. An inquisitive player is rewarded by finding small amounts of more exotic ammunition and some chems on the upper floors, as well as a Nuka-grenade (in a wooden box by a desk near the SW corner), electron charge packs in buckets, as well as access to ammunition boxes and Nuka-Cola vending machine.
An EnclaveVertibird is on the highest level, inaccessible to the player. If fired upon, it will catch on fire and then attempt to flee shortly before exploding.
The level just below the Vertibird is inaccessible. Accessing it on the PC version via console commands reveals that there are missing walls and no loot (except for the randomly-generated contents of a few desks and/or filing cabinets).