No filter recommendations other than the usual B&W filters and maybe a grad ND, but when I was photographing in Tampere, Finland for a few days one summer, I really liked the light, particularly late at night. I ended up losing a lot of negs to vignetting problems, because I was using a filter holder I hadn't tested before (oops!), but it was neat to be out with the 8x10" Gowland at 10 p.m. photographing.
Do be sure to take some faster film along as well. Even though the days are long in August, there is no guarantee in either of those places that you will get much sunshine!
I agree with David though, it's amazing to be able to go on a hike late at night.
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