Foreigners' Registration Office A laborious way of getting a permit for Sikkim is to fill an application form and get a memo number at this office, then head across town to the District Magistrate's Office for further formalities. Total time is about two hours. It's simpler and quicker to get the permit (free; take one passport photo and copies of your passport and visa) at the Rangpo or Melli border, or the Sikkim Tourism offices at Siliguri or Bagdogra airport.
Office of the District Magistrate You can get a permit for Sikkim here if you come with a completed form and memo number from the Foreigners' Registration Office. Head to room 4 upstairs. Bring your passport, photocopies of it and your visa, and two passport photos.