Cross-country skiing is a popular winter activity in the French Pyrenees, and there are several trails that are suitable for multi-day trips with overnight camping. Here are a few options:

1. The Trans-Pyrenees Trail: This is a long-distance ski trail that runs the length of the Pyrenees. You can choose a section of the trail to ski in winter, such as the section between Luchon and Cauterets. This section is approximately 70km long and takes 3-4 days to complete. There are several mountain huts and refuges along the way where you can spend the night.
2. The Haute-Route Pyrénées: This is a popular ski touring route that takes you through some of the most scenic areas of the Pyrenees. The trail starts in Cauterets and ends in Bagnères-de-Luchon, covering a distance of approximately 70km. The trail takes 4-5 days to complete, and there are several mountain huts and refuges along the way where you can spend the night.
3. The Néouvielle Nature Reserve: This is a beautiful area in the heart of the Pyrenees that offers many opportunities for cross-country skiing. There are several trails in the area that are suitable for multi-day trips with overnight camping. The Refuge de la Glère is a popular place to stay overnight and is accessible by skiing or snowshoeing.

It's important to note that cross-country skiing in the Pyrenees can be challenging, and it requires proper gear and experience. Make sure you are prepared for the conditions and check the weather forecast before setting out.
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