For Sikkim you will need a trekking permit. If you have a visa for Bhutan, you'll also need a transit permit to cross the border. This permit is available from the Ministry of External Affairs. Consult the nearest high commission, embassy or consulate in your own country for further details. Public Holidays India has a wide range of holidays and festivals, due to its religious and regional variations.
Most Indian holidays follow the lunar year, so the dates vary from year to year.
It is best to check the dates of the public holidays with an Indian embassy or consulate before traveling. The peak tourist season is from mid-September through to March, as the cooler winter months are from November to February. But as long as you take the weather into account, India is a year-round destination. Expect crowds at popular tourist spots and be sure to make reservations well in advance. September to March is the best time to visit the plains and the southern regions.