This is a webquest introduction to navigating at sea. The link goes to a Smithsonian animation that shows the typical, pre-GPS method -- using a sextant -- to calculating location on Earth's surface.
Click here for the Question Sheet!
This activity is a great introduction for students interested in knowing how to figure out where they are when at sea. Crude sextants can be constructed using paper, a weight, a string, and a stiff object, such as a ruler.