Open up, start up or launch, would be appropriate antonyms for the phrase "close down," which signifies the cessation of an activity, a location or a business. Opening up means to commence a new enterprise or event. Starting up is another expression that relates to the initiation of an enterprise, typically in the business sector. Launch refers to initiating a new product, service or activity. The antonyms for closes down are vital to understand in order to represent something that characterizes a new beginning, stimulation and continuation rather than cessation, end and termination.