Distribute a handout where one side has a description of a famous explorer, along with his accomplishments and the region he explored and the other side has a list of names of explorers. The students have to match the explorer with his description. Divide the students into groups or allow them to complete these tasks individually. Award a small prize, such as a "no homework" pass, to the first group or first few students who correctly complete the task.
For younger students, hand out a word scramble or a word search in which they either need to unscramble or search for the names of famous explorers, lands they discovered and other key terms related to the topic. With a more advanced group of students, you could create a crossword puzzle where the students need to use the hints and clues on the page to fill out the entire crossword puzzle.
Take the students to the computer lab and divide them up into groups if there are not enough computers for everyone in the class. Have them take an online explorer quiz, such as the one located on Think Quest (thinkquest.org). They will have to answer questions such as "Who was the first European to sail down the Mississippi River from the Great Lakes to the Gulf of Mexico"? and "Who was the first European to explore the mainland of America after the Vikings?"
Introduce longitude and latitude by comparing it to current navigational systems. Assign each student or each group of students a different journey to trace. Using research tools available on the Internet and in the library, have the students find several exact points of latitude and longitude that the explorers in their journey were traveled. Give them a target number of points to reach and award a small prize to the first team to finish the hunt.