In 2002 I was working with a startup (that later failed). The office was in the basement of a warehouse, because they got cheap rent. The office itself wasn't terrible, decent offices and equipment. Since it was a basement there were obviously no windows. We were working 80-100 hours a week, often sleeping in the office. We had a really bad flood a few weeks before our launch date. We got (most) of the water out, but the walls started molding before they could get everything fixed. I bought my own hepa-filter and eventually "took a break" because I couldn't take anymore.