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!
That didn't even make that much sense in English.