When traveling around London try off-peak Day Travelcards. They cost £5.10 and can be used after 9:30 a.m. for unlimited travel for the rest of the day on the Tube or the Dockland Light Railway.
Berlin has a one-day unlimited travel ticket on their public transportation system, the BVG. Costs 6.10 euros for travel in Zones A and B, where most tourist attractions are found.
Copenhagen has 1,300 free bicycles for use until December. Look for City Bike Parking places in the city center. You need to deposit 20 kroner (about $3.50) then off you go. Don’t forget to return the bike to get your deposit back.