The Elevator

The elevator in the apartment building in which Sheldon, Leonard and Penny live in had been out of order for over two years, ever since the time Leonard tested out an experimental rocket fuel formula which began to explode, with Sheldon saving Leonard's life after he tried to take outside by going down the elevator but was stopped by Sheldon closing the elevator after taking Leonard out. Ever since Penny moved in, she has needed to take the stairs instead using the broken elevator. Many people new to the building have tried to go in the elevator, before realising it is broken, such as Zac and Beverly Hofstadter, although she was merely wondering why it hadn't been fixed. Howard once tried to fix the elevator, but upon inspection gave up immediately.