Catskill Mountain 3500 Club

The Catskill Mountain 3500 Club, incorporated as the Catskill 3500 Club and often just referred to as the 3500 Club, is a peakbagging organization for hikers in the Catskill Mountains of New York. Those wishing to become members must climb the 33 of the 35 Catskill High Peaks currently open to hikers, and, in a departure from the requirements of most other such clubs, climb Slide, Blackhead, Balsam and Panther mountains again in winter, which is defined by the club's by-laws as the period from December 21 to March 21 regardless of the actual occurrences of the winter solstice and vernal equinox in particular years.

Source: Wikipedia — Catskill Mountain 3500 Club (CC BY-SA 4.0)