Indeed, we would need either "the" or "a," and really only "the" makes sense.
"Where's the metro" isn't accepted as well, though. I'm going to report this.
can someone please fix this please, it's been at least three months and it's still wrong. the further i get in this course, the more ridiculous garbled translations i have to memorise in order to please the course designers and it's getting really, really annoying
"Metro" is not the only acceptable translation. "Subway" and "underground" should also be acceptable. It all depends on where the English-speaking person lives.
"Where is an underground?" Should be a possible translation, not only "subway".