India boasts some of the most stunning natural landscapes in the world, and trekking is a popular activity to explore them. With a wide range of options, the country offers treks suitable for all experience levels.

Some treks can be lengthy, spanning several days, but the breathtaking views and unique cultural experiences make them all worthwhile.

1. Dhappa - Lawan Glacier Trek | 103.5 km

This trek is a 103.5-kilometer out-and-back route located near Munsiari, Uttarakhand. It is a challenging trail that should be attempted only by seasoned explorers. 

When trekking, you may meet other hikers, making it more enjoyable. This trail is excellent for birdwatching and camping, too. The best times to go are June to October. However, the terrain is challenging, so carry proper gear, research beforehand, and be cautious.

• Distance: 103.5 km
  
• Altitude: 6,916 m
• Best Time to Visit: June to October
• Duration of the Trek (including travelling): 14 days
• Difficulty Level: Hard

2. Teejam - Liam Trek | 116.7 km

The Yangchar Glacier is a challenging region with rugged terrain, unique wildlife, and breathtaking landscapes. It was once a bustling trade hub between Tibet and India and remains a popular destination for adventure seekers and nature enthusiasts.

• Altitude: 8,889 m
  
• Best Time to Visit: May to June & September to October
• Duration of the Trek (including travelling): 10 days
• Difficulty Level: Hard

3. Tantse Gompa Trek | 121.5 km

The Zangla to Tantse Gompa trek in the Zanskar region of Ladakh offers stunning views of the Zanskar Range and a chance to experience the area's unique culture and ancient monasteries.

Starting from the village of Zangla, hikers will cross the 16,800 feet high Shapodakla Pass and descend into the Tangyar valley, leading to the Tantse Gompa monastery, which is known for its antique manuscripts, thangkas and exquisite paintings.

• Altitude: 9,224 m
  
• Best Time to Visit: May to September
• Duration of the Trek (including travelling): 5 days
• Difficulty Level: Hard

4. Tawaghat - Darma Valley Trek | 127.5 km

Darma Valley in the Himalayas is famous for its diverse range of flowers, especially orchids, and offers breathtaking views of the Panchachuli peaks.

The journey towards the valley is beautiful, with picturesque ancient towns, flowing streams, and vibrant flora. It is advisable to plan a visit between April and September when the weather is milder. To reach the Dharchula hamlet, it is best to travel by private vehicle.

• Altitude: 5,941 m
• Best Time to Visit: April to September
• Duration of the Trek (including travelling): 7 days
• Difficulty Level: Hard

5. Darma Valley Trek | 136.5 km

The Darma Valley is situated between Lassar Yangti Valley and Kuthi Yangti Valley. It provides stunning views of the Panchachuli Alps and is renowned for its wide range of flora and fauna, especially orchids.

As public transport is limited in the area, it's recommended to have private transportation to reach the valley.

• Altitude: 6,612 m
  
• Best Time to Visit: June to October
• Duration of the Trek (including travelling): 10 days
• Difficulty Level: Hard

6. Udaipur - Kang La Pass Trek | 142 km

The Kang La Trek is a challenging hike spanning India's Himachal Pradesh and Ladakh regions. It offers stunning views of snow-capped peaks, glaciers, glistening lakes, and lush green valleys.

Proper gear, supplies, and a knowledgeable guide are necessary for experienced and physically fit hikers. It is an unforgettable journey that will test your limits but reward you with a lifetime experience.

• Altitude: 3,538 m
  
• Best Time to Visit: May to October
• Duration of the Trek (including travelling): 12 days
• Difficulty Level: Hard

When it comes to embarking on a long trek in India, it is important to ensure that you have all the essentials to make your journey comfortable and safe. 

Here is a list of essentials that you should consider packing for your longest trekking route:

• Good quality trekking shoes
  
• Comfortable and breathable clothing, including warm layers for the night
• A sturdy backpack with a rain cover
• Tent, sleeping bag and sleeping mat
• Water bottle and water purification tablets
• First aid kit with essential medicines
• Headlamp or flashlight with extra batteries
• Maps, compass and GPS device
• Sunscreen, sunglasses and sun hat
• Insect repellent and mosquito net
• Emergency whistle and signaling mirror
• Multi-purpose knife or Swiss Army knife
• Cash, ID card and travel insurance
• Snacks and high energy food like nuts, energy bars and dry fruits.

Note: Keep in mind that the specific items you need may vary depending on the trekking route and duration of your journey. 

India has some of the most breathtaking trekking routes in the world, offering an exceptional blend of adventure, cultural diversity, and natural beauty. It has many options for those looking for a challenging and lengthy trek, from the snowy Himalayan peaks to the lush valleys of the Western Ghats.

Whether you are an experienced hiker or a first-timer, India's most extended treks promise to create memories that will last a lifetime.