Permit & Paperwork

(A) For Indian Nationals:

A trekking permit is required inside Barsey Rhododendron Sanctuary and can be obtained at the Hilley Forest checkpost. Two recent passport-size photos, One personal photo ID card with address proof in it (Aadhar/Driving Licence/Voter ID/Passport) along with photocopies of the same are to be submitted along with a self-declaration at Yuksom police outpost. Below is a handy guide for those having plans for additional holidays/destinations in Sikkim. Even Indians need a Protected Area Permit (PAP) for visiting North Sikkim or Nathu La.
http://www.sikkimtourism.gov.in/Webforms/General/faq.aspx

(B) For Foreign Nationals:

Any foreigner (some relaxation to Nepalese and Bhutanese citizens) will require an Inner Line Permit which is recently renamed as Restricted Area Permit (RAP) to enter the boundary of Sikkim.
http://www.sikkimtourism.gov.in/Webforms/General/Essential%20Information/Entry.aspx

Nationals of Bangladesh, Pakistan, Myanmar, Nigeria and China can only apply for ILP/RAP through the Ministry of Home Affairs, Government of India, New Delhi.
Any other foreign national with the strength of a valid Passport and Indian visa can obtain the ILP (RAP), Free of cost, at the below checkpoints while entering Sikkim.

1) Assistant Director– Tourism Department, Melli, Near Melli Police Check Post, South Sikkim, Mobile No: 9775453611, 03595-248536, PLS NOTE: ILP issuing time is from 8 am to 8 pm every day (Though we struggled to keep them stay after 6 pm!)- On the way to West Sikkim (Yuksom, Pelling, Hilley, Uttarey etc)

2) Assistant Director, Tourism Department, Sikkim Tourism Office, Rangpo, East Sikkim phone no: 03592-240818 – On the way to Gangtok and East/North Sikkim.

If you produce a proper itinerary (additionally if any supporting booking documents) then the authority will usually issue an ILP up to 30 days initially. It can be extended to another 30 days but to get an extension you need to exit Sikkim and apply again when you re-enter.
Travellers who arrive initially in Darjeeling (state of West Bengal) have to get the permit from the above two check posts. There is a shorter route from Darjeeling to Jorethang via Jamuney (40 Km, 2 hours maximum) but foreigners are not allowed to enter Sikkim along this road. You have to go via the Darjeeling – Jorbanglow – Teesta route.
You may obtain an ILP online, but that doesn’t make much sense. This is a document valid only when it is signed physically in any of the above two offices. It takes 10/15 minutes to process the ILP at Melli/Rongpo with the strength of your valid passport and Indian visa.

Foreign national tourists who wish to trek to Dzongri/Goecha La, Singalila/Phoktey Dara (Barsey Rhododendron Sanctuary), Round Singalila Dzongri (Uttarey to Dzongri) will require an additional permit called Protected Area Permit (PAP, often referred as Trekking Permit). This is issued to a minimum group of 2 persons or more from the following office on the strength of signed and valid ILP/RAP.
Adventure Cell of Tourism & Civil Aviation Department, Govt. of Sikkim, Gangtok
http://www.sikkimtourism.gov.in/Webforms/General/pdf/RAP.pdf

Important Points to Note

Trekkers must carry a copy of their photo ID for entry at forest check posts on the trek.
At the base camp, your stay will be arranged in lodges which is going to be your extra cost.
On the trek, you will be staying in a ten & homestay.
Anything beyond one bag is chargeable at Rs 500 per luggage.
No Trekking Gears is provided by Mochilero Aventura.

Note for Foreigners: Foreigners have to register for the trek in a group of 2 and above. Along with that, there are different permits to be obtained for your trek.

The ILP (Inner Line Permit or Sikkim Permit) for foreigners – Check this link for more details – http://sikkim.nic.in/homedept/ilpfaqs.htm. You can obtain these outside the Bagdogra airport or at the check post before entering Sikkim from Siliguri.
Trek permit for all trekkers – Obtained at the forest check post at Yuksom. The fee varies for students (ID card required), regular Indian citizens (ID proof required) and foreigners.
Special trek permit for foreigners – Foreigners need to obtain a special permit at Gangtok to trek in Sikkim. The charges for obtaining the permit will be Rs 2,500 per person.
Citizens of China and Myanmar are not permitted to trek in this area.