Thalay Sagar, Mountain summit in Uttarkashi district, India.

Thalay Sagar is a 6,904-meter peak in the western Garhwal Himalayas featuring steep rock walls and a demanding north face within the Gangotri massif. The summit sits at a considerable height in this high-altitude mountain chain.

Thalay Sagar was first climbed on 24 June 1979 by an Anglo-American team of Roy Kligfield, John Thackray and Pete Thexton, who went up the northwest couloir and ridge and crossed the shale band of the North Face. Foreign climbers had been barred from most of the Garhwal region until the late 1970s. Ascents of the peak later received the Piolet d'Or in 1999 and 2017.

The mountain stands near Gangotri, a sacred pilgrimage site where the Bhagirathi River originates, making it part of a spiritually significant region for Hindu traditions.

The climbing season runs from June through September, requiring around 40 days of expedition time from Delhi. Proper mountaineering experience and acclimatization are necessary for this high-altitude ascent.

Thalay Sagar's north face has been climbed by five different routes, and the shale band near the summit is the key obstacle on the most direct ones. The first route to break straight through it, rather than finishing on a ridge, was the Australian Route of Andrew Lindblade and Athol Whimp: 1,400 m of climbing graded VII 5.9 WI5, awarded the Piolet d'Or in 1999.