We stayed with a friend in Berlin who is a keen cyclist. He took us on several rides within the city, along canal and riverbank paths as well as on the road system. By bike you can cover larger distances than walking, and experience more of the atmosphere than on public transport. Other vehicles respected us as fellow road users.
We also took the bikes on the train to Potsdam (special carriages, look for the cycle symbol) and cycled round the town and Park Sanssouci. Although cycling in the park is not strictly allowed, it is extremely large and would be difficult to take in all the small palace buildings in one visit on foot.
As our host had the bikes we did not have to look for hire shops, but I am sure they exist as it is a cycle friendly city - or take your own with you!
Is this your business?