Boston Area is very safe, particularly Cambridge and you should have no worries walking anytime of day or night. I generally feel safer in Boston than I do in Berlin or Munich. In fact, I think you’ll find it downright pleasant that time of year.

You still need to be vigilant, as you would be in any dense city. For example, There’s some homeless that hang out in the Central Square area and a few of them have been known to verbally harass passerbys. But after living here for a decade, besides the occasional person asking for money, I’ve never had anything resembling an issue.

Also, with you coming from Germany, we know our trains are an absolute embarrassment right now. Particularly the Red Line. We’re working on it.

Since you’re only here for a week - and if you were worried about traveling at night, you can always call an Uber. Distances in Boston a relatively short, a nighttime Uber from downtown to Cambridge would be like $15. I know your student, but I don’t know what your budgeting looks like. Just something to think about.