Hi, While in Manali, apart from the local sightseeing, you can go for a day trip to Rohtang Pass, go for the Jogini Falls Trek or visit Manikaran and Vaishno Devi. It doesn't snow in Manali in September. Snow is generally around late December or early January only. Same with skiing, it happens around Dec-Jan only. However, there are other adventure activities like trekking and paragliding. However, do check with operators beforehand. Hope this helps!