Kellas was also a noted mountaineer in his own right. He had made at least ten first ascents of peaks over 6,100 m (20,000 ft) including Pauhunri, 7,128 m (23,386 ft), in Sikkim, which was the highest peak climbed up to that point, although this was only discovered 80 years later. He reached the summit on 14 June 1911, and this world summit record was only broken in September 1928 with the ascent of Lenin Peak.