The gigantic castle he erected at Osaka was the biggest Japan had ever seen, requiring a work force of 30,000 men.
The biggest castle Japan had ever seen was erected in Osaka, requiring over 30,000 men to complete.
It is a demanding method, requiring specific skills (such as fluency in the language of the participants) and general self-awareness to maintain the fine balance between seeing things as others see them and identifying their perspective wholly with one's own.