It's absolutely safe to travel to Kashmir in December as it is the beginning of the winter season. Do have a check on the weather before your start with sightseeing. Most of the roads will remain open in December and hence reaching to popular destination like Sonamarg, Gulmarg and Pahalgam will not be a problem. You can spend two nights in Srinagar, two nights in Pahalgam and one night each in Sonamarg and Gulamarg or do day trips to these places.
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