A mini-computer linked to GPS is providing tourists in Berlin with a guided tour of the city. Combined with pictures and audio files is a lesson in history. Little remains, for example, of the Berlin Wall, but the GPS shows exactly where it stood and the software tells what happened there. We look at wind turbines producing greener energy, and also how the biofuel of the future will come from sticks and stems. Meanwhile medical researchers from the Genetic Eye Foundation are developing a bionic eye that can help severely blind people navigate around large objects. Also, reusing silicon wafers; historic preservationists in England put solar panels on a castle because global warming is a greater threat to the national heritage; and, in confirmation of that threat, we look at disappearing sea ice.