I think you have to explore the whole world with one character as well. You cannot split the exploration between different characters for the World Traveler.
"Don't believe in the you that I believe in. Believe in the you that you believe in." - TTGL
Great words to live by. But I go with. "Do your best at everything. Always be strong, be fierce, and don't let others hold you back. Most of all don't hold yourself back." - K