Answer: explorers

AnswerCrossword Clue
EXPLORERSShackleton, Scott, and Hillary.
EXPLORERSColumbus, Clark, Armstrong et al.
EXPLORERSDe Soto, Cabot, etc.
EXPLORERSLewis and Clark, e.g.
EXPLORERSThey expand horizons
explorersA person who explores an unfamiliar area; an adventurer
explorersEXPLORER, one who explores (to examine thoroughly)