English
While many books in the Choose Your Own Adventure series utilised horror elements, only a few of the books were explicitly horror-themed.
Vampire Express is one of the more obvious horror entries, but it's also one of my favorite books in the series. The atmosphere, artwork, and plot are well executed, and there are a lot of memorable moments, no matter which path you take.
The book begins with you taking a train into the Carpathian mountains (an area with historic connections to vampires) to meet your uncle, the world's most knowledgeable expert on vampires. He's planning an expedition that will scientifically prove that vampires actually exist.
The book never bothers to explain what your parents think of sending their kid on a potentially lethal mission like this, but that's par for the course in the CYOA universe. The artwork depicts a kid that looks maybe 15 or so, so it's reasonable to speculate on the fitness of the parents.