"podróż" is female?
Yes. Count it as an exception, although of course there will be more of them.
Can't "interesujące" also mean interesting? My Polish teacher always uses it, but Duolingo marked it as incorrect
That was because of the form. "interesujące" is either neuter singular or not masculine-personal plural.
"podróż" is feminine, therefore: interesująca podróż