Looking for a horror film/thriller title?

Hey, I'm looking for the name of a movie. The genre was something like horror/thriller.

It's about a vacation apartment that two strangers share because of a mistake. At one point, the woman goes into the basement (I think because she hears noises) and finds a secret tunnel. There's some kind of hybrid of human and monster that captures her and locks her downstairs. Some time later, another woman arrives in the apartment, also goes into the basement, and finds the woman imprisoned.

I can only vaguely remember it. Does anyone know the film?

I think it's called something like "Beast" or something