YOU SAID:

I can't imagine how hard it must have been to walk around the whole world!

INTO JAPANESE

私は全世界を歩くのがいかに難しいか想像できません！

BACK INTO ENGLISH

I can not imagine how hard it is to walk the whole world!

INTO JAPANESE

私は全世界を歩くことがどれほど難しいか想像できません！

BACK INTO ENGLISH

I can not imagine how hard it is to walk the whole world!