An historical reference, along with a solution and interesting links for the Konigsberg bridge problem is found at this site:
http://mathforum.org/isaac/problems/bridgesol1.html
This site provides a thorough overview of the Traveling Salesperson Problem (TSP):
http://www.nist.gov/dads/HTML/travelingSalesman.html
This site provides Graph Theory tutorials:
http://freecodecamp.org/
Here is a site on how to construct a Mobius strip:
https://www.wikihow.com/Make-a-Mobius-Strip