Writing a horror story...

When I get an idea for a story, I always get a glimpse of the story, like a film clip in my head. I almost never know how to use the idea, or in which genre the idea fits in. I write it down, and move on.
But about a week ago something different happened. I was sitting in the train early in the morning, travelling from Aalborg to Hobro where I an being trained to be an Occupational therapist. I was looking out the window, when suddenly the black horizon was broken by the sun of the breaking dawn. It shined trough the morning fog, in such a way only a horror film is able to portray it, like after the hero has just escaped the evils of the night.
This inspired me to try and write a horror novel.
But what is a horror novel? And is it at all possible to classify a story like a pure horror story? Well, I personally don't think so, and I think I would get bored reading or writing such a story.
I need to spice it up with some drama, or some other kind of story that can keep the characters moving forward. This is for me always the hardest part. What should the drive of the characters be? Will it be enough to keep the story alive and interesting all the way trough?
This question, is what I am going to work on in the next couple of days.
So far the story is taking place in Europe, where a young man and one of his friends are on a ghost hunt all over Europe (interrailing/Eurorailing). The trip is arranged by an international ghost-hunting organisation. They have planned to travel to old and new ghost sheeting places in Europe (like; Transylvania Dracula, Catacombs in Paris France, Sedlec Ossuary, Czech Republic). They travel by train, but the trip does not go as planned...

Well, more to come :-)
If you have any ideas, leave a comment..
Thanks...