Oh, we had one of those once, over in a park. Another time we had like a carnival day, next to the office, so we could still go in and out, but i almost got heatstroke being outside most of the day.

Geez, they lock you up inside all year, then expect you to go outside? How is this in your job description? I would tell your boss i had reservations (not specific) about spending the day outside and that i would volunteer to remain in the office.