Solo female looking at a 2 day stopover - any issues I should be aware of?

I like to walk in new cities to get a feel for things, would this be unsafe? I am generally uncomfortable with taxis as a single woman, so would prefer to avoid them unless necessary.

I presume shoulders and knees covered is preferable? Or can one be slightly cooler (sleeveless -not strappy tanktop- and above the knees shorts) without being considered offensive?