The BridgesOfKönigsberg is a classical problem in GraphTheory.
There is a pond illustrating the BridgesOfKönigsberg at CanterburyUniversity outside the ComputerScience department.
See http://www.jcu.edu/math/vignettes/bridges.htm
3 pages link to BridgesOfKönigsberg:
http://www.jcu.edu/math/vignettes/bridges.htm