I'm in the US. I don't know whether a (presumably) unpaid internship (or one for which I may have to pay a fee, even) requires a work permit. The latter situation is more like school. And as a US-passport holder, I don't need a residence permit for 90 days as a tourist, but whether the internship counts as work or education I really don't know, and I have no idea where to look that up.
Re: Here via a friend