It is a large, open square with homes with the administration building and the Harp bar ringing it. The town well is close to the entrance of the reactor. It gives access to the junkyard near the brahmin pens and the main reactor doors.
The manager's office is where Harold and his assistant Lenny reside, and run the small settlement. They are having problems with Vault City, but cannot get near enough to bargain for the needed part, as they are being shot at at sight. Harold is a very trusting individual considering his life experiences, and Lenny can be recruited as a companion.
Here one should talk to Harold before entering the powerplant, as there must be some parts that need fixing, and Harold can explain which are needed.
Also, a requisition form can be found here for legally acquiring from the supply room in the powerplant.
Big Book of Science - On the shelves in the Manager's office.
The Gecko settlement appears only in Fallout 2.