There is nothing that fascinates me about the dark. For the most part, the same things that are in the dark were also in the light before it became dark. :)
I think it isn't so much a fascination with the dark as a fear of what may be lurking in the dark. We all know people with less than good intentions often choose to do their deeds under cover of darkness. It's easier to sneak up on people or to steal something sight unseen because of darkness. As a result, people are less confident in the dark.
There are also a lot of people who indulge in the occult or things that are mysterious or even evil. What they don't understand is that by thinking about these things, worrying about these things, they give them energy and invite these things into their lives. Such things do not have to be invited twice, and are usually early rather than late to accept any invitation.
Many bad things have happened in the dark over the centuries, and people naturally worry that one or another of those things might happen to them in the dark. Whether it's a burglary or some other illegal act, an accident because one can't see where they're going, or something from the underworld, knowing that bad things have happened to others, or even perhaps to oneself in the past, makes people nervous about the dark.
Fortunately we have some great flashlights on the market, and I have an excellent flashlight on my smart phone. The dark is useful and desirable in the right conditions, but knowing that bad things have happened to people in the dark naturally makes most people concerned they may have a mishap in the dark themselves, if they venture into it. There are precautions one can take, and I certainly recommend making use of them.