To this day it still amazes me how much ground one can cover, in such a short amount of time, almost effortlessly via bicycle. And so, while one is traveling, it is worthwhile considering the rental of a bicycle. Or if traveling by motorcoach/auto, bringing a bicycle with them. If space is an issue, there are several folding bikes on the market.
Recently we spent about 4 days in San Francisco. It seemed there were bike rentals everywhere. A ride from Fisherman's Wharf, across the Golden Gate Bridge and into Sausalito is only about 8 miles. From there if one prefers a ferry can be used for the return trip. As a little side note we tried a tandem bike. This was not nearly as easy as some people make it look. It's like riding a bike with a large amount of weight on the back cargo rack. Needless to say we switch to two separate bikes.
Here are a few more examples which I'm actually stealing from my friend's Beer Brewing Blog (go figure) -
Their bicycle tour of Stanley Park, Vancouver
Cycling around Paris and Napa Valley Wine Tours
So the next time you are going to rent a car in a foreign city to battle traffic and pay for parking, consider the bicycle.