Atop the summit of the 13,796-foot-high Mauna Kea in Hawaii sit the world's biggest telescopes: the 10-metre KECK twins. Mated to one of them is the world's most powerful spectrograph, DEIMOS. On this trip to the mountaintop, we meet the astronomers who built these magnificient instruments and find out how they are being used to count galaxies one slice of the universe at a time. It's a story of iconoclastic astronomers who broke with tradition to build the KECKs. Little did they know at the time the crucial role it was going to play in deciphering dark energy and become a key tool for cosmologists.