An international application is usually filed directly (known as a "direct filing") with the International Bureau of WIPO by the applicant. WIPO's office is located at:

34, chemin des Colombettes, in Geneva, Switzerland.

An electronic filing (e-filing) service is also available for the Application of International Registration (DM/1) at
www.wipo.int -> IP Services -> Designs (Hague System) -> E-filing/Forms 

An international application may also be filed, at the option of the applicant, through IPOS ("indirect filing").
Upon receipt of the international application and the payment of fees (including a transmittal fee), IPOS will forward the international application to the International Bureau.