In 1870 at the age of twenty he was made a member of the Alpine Club. Coolidge was one of the great figures of the so-called silver age of alpinism, making first ascents of the few significant peaks in the Alps that had not been climbed during the golden age of alpinism. On many of these climbs he was accompanied by his aunt, Meta Brevoort, and a pet dog, Tschingel, given to him by one of his guides, Christian Almer.