Could it be a shaft?, perhaps for an elevator, not looking like cardboard..almost looks like cement blocks or bricks. There also appears to be 2 window like openings.
Norbulk Shipping NB LTD does not have any Key Executives recorded.
https://www.bloomberg.com/research/stocks/private/snapshot.asp?privcapId=331620150
Will keep looking but this is the result so far.