If I have seven bridges in a town can I start at point A and only cross each bridge once and still return to point A?
It depends on how the bridges are made.
If all bridges link places that are not otherwise accessible, it would not be possible to make a return trip without crossing at least one bridge more than once because one needs to go and come back in an even number of crossings.
It would, however, be possible if at least one bridge is a by-pass, namely it works only as a short-cut. In this case, one can make the return trip on land.
There is a similar mathematical problem on topology which inspired the mathematician Euler to work on topology. Check the following link or other articles:
http://mathforum.org/isaac/problems/bridges1.html