1. Singalila Kanchenjunga Trek
Some of the most famous views of Kangchenjunga are from the hill station of Darjeeling and Antu Dada of Ilam, Nepal. The Darjeeling War Memorial is among the most visited places from which Kangchenjunga is observed. On a clear day it presents an image not so much of a mountain but of a white wall hanging from the sky. The people of Sikkim revere Kangchenjunga as a sacred mountain. Permission to climb the mountain from the Indian side is rarely given.
Due to its remote location in Nepal and the difficulty involved in accessing it from India, the Kangchenjunga region is not much explored by trekkers. It has, therefore, retained much of its pristine beauty. In Sikkim too, trekking into the Kangchenjunga region has just recently been permitted. The Goecha La trek is gaining popularity amongst tourists. It goes to the Goecha La Pass, located right in front of the huge southeast face of Kangchenjunga. Another trek to Green Lake Basin has recently been opened for trekking. This trek goes to the Northeast side of Kangchenjunga along the famous Zemu Glacier. The film Singalila in the Himalaya is journey around Kangchenjunga.
Source: wiki Singalila Kanchenjunga Trek
2. Zanskar Frozen River Trek
Lower (northern) sections of that gorge are popular in summer with tourists making rafting trips, typically from Chiling to Nimmu. In winter when the road to Zanskar is closed by snow on the high passes, the only overland route to Padum is by walking along the frozen river, a multi-day hike that is now sold as an adventure activity called the Chadar (‘ice sheet’) Trek. This trek will eventually be rendered obsolete once the road from Chiling to Padum is completed.
Source: wiki Zanskar Frozen River Trek
3. Gomukh Tapovan Trek
The most well known tapovan in India is the area above the Gangotri Glacier at one of the primary sources of the Ganges, in Uttarakhand, India. At the foot of Shivlingpeak, a barren area at about 4,463m (14640 feet) elevation, is a seasonal home to several sadhus living in caves, huts etc. and it has become a trekking destination also. The trekking usually starts from Gomukh and the trek was considered moderate to difficult  prior to the destruction of much of the trail from Gangotri to Gamukh by the 2013 North Indian Floods. Tapovan area is base camp for several mountaineering expeditions including Shivling peak, Bhagirathi peak etc. Tapovan area is full of meadows, streams and flowering plants and the meadows are considered as one of the best high altitude meadow in India. There is also a place named Nandanvan near Tapovan, and Nandanvan is also trekked by trekkers and pilgrims. Nandanvan is also a spacious meadow located at the base of Bhagirathi massif.
Source: wiki Gomukh Tapovan Trek
4. Markha Valley Trek
As Markha Valley is located near to Tibet, tourists can feel the touch of Tibetan culture in the lifestyle of people living there. Markha valley gets heavy snow fall during winter and because of that it remains isolated for most of the months in a year.
Markha Valley trek also known as a ‘tea house trek’ is a standout amongst the most mainstream treks in Ladakh.Markha Valley trek also known as a ‘tea house trek’ is a standout amongst the most mainstream treks in Ladakh – it is a flawless mix of wonderful trans-himalayan scene with Ladakhi towns. It spills the opportunity to climb the highest point of two high passes, Gandala La (4800 m) and Kongmaru La (5150 m) and gives you an exceptional view of Ladakh and Zanskar ranges, the 21,000 ft Kang Yissay and the 20,086 ft Stok Kangri tops.The another thing to do in ladakh is leh ladakh bike trip which can not be missed.
source: wikitravel Markha Valley Trek
5. Zanskar Trek
Zanskar or Zangskar is a subdistrict or tehsil of the Kargil district, which lies in the eastern half of the Indian state of Jammu and Kashmir. The administrative centre is Padum. Zanskar, together with the neighbouring region of Ladakh, was briefly a part of the kingdom of Guge in Western Tibet.
The Zanskar Range is a mountain range in the Indian state of Jammu and Kashmir that separates Zanskar from Ladakh. Geologically, the Zanskar Range is part of the Tethys Himalaya, an approximately 100-km-wide synclinorium formed by strongly folded and imbricated, weakly metamorphosed sedimentary series. The average height of the Zanskar Range is about 6,000 m (19,700 ft). Its eastern part is known as Rupshu.
It also separates Kinnaur District from Spiti in Himachal Pradesh. The highest peaks of Himachal are in the Zanskar Range.
Source: wiki Zanskar Trek
6. Kuari Pass Trek
Well-liked among the trekkers worldwide, Kuari Pass Trek offers startling vistas of the snow capped peaks of the Greater Himalayan Range. Also named as Lord Curzon’s trail, this trek goes through the lush valleys, thick forests and small villages. On reaching Kuari Pass, the trekker is rewarded with panoramic views of the magnificent peaks of Nanda Devi, Chaukhamba, Kamet, Hathi-Ghodi Parvat and Dronagiri.
7. Pin Parvati Pass Trek
The Pin Parbati Pass is a mountain pass in Himachal Pradesh, India.It was first crossed in August 1884 by Sir Louis Dane in search of an alternate route to the Spiti valley. This pass connects the fertile and lush Parbati valley on the Kullu side with the Pin valley on the Spiti side.
It is a popular trekking route today though still rarely visited. This trans-Himalayan trek is the shortest route between the Kullu and Spiti Valleys. Once over the Pin-Parbati pass (5319m), there is a complete change in landscape – the mountain slopes immediately turn barren and rugged. The prevalent culture of the inhabitants also changes from Hinduism on the Kullu side to Buddhism in Spiti.
Often referred to as the most challenging trek in the Indian Himalaya, it’s more than worth the effort. The best time to go for this pass from Mid June to July end and September to mid October. It is best to avoid especially August month where there is a lots of rain during monsoon. The route goes along the Parbati River up to Mantalai Lake and from here its steep ascent to the pass. The upper most of Parbati valley comes under Great Himalayan national park.
Source: wiki Pin Parvati Pass Trek