CERN's computer room. It was once full of mainframes, even a Cray (which had the processing power of 50 mainframes or about a tenth of my laptop!), and now has thousands of PCs and tens of thousands of CPUs.
Even with all those CPUs, only 20% of CERN's processing takes place at CERN. The rest takes place on the Grid -- other connected computers located around the world. Tote runs his work and stores the results on computers at Rutgers and Fermilab.
This is super nerdy, but it was interesting to see how the PCs were cooled. Rather than putting them all in a big, air-conditioned room, as was done for mainframes, the aisles between PC racks are air-conditioned, so the PCs take in cold air from the front.
Also nerdy: there was once a measure of computing power called the CERN Unit -- roughly the power of a mainframe.