Use much more light.
If you want to create total darkness, here's a trick:
You create a black fog area in the place you want to be dark, and use lights normally.
This way the player won't see things that are far, but will be able to see what's just around them.
Also, the black fog has a much more natural feel than straightforward darkness. Just make sure to adjust it correctly. I use Start=0, End=12 and FalloffExp=1, but it depends on preference.
To make your maps more interesting, remember to also use particles and decals. All of these (fog as well) are in the left toolbar in LevelEditor.
Make sure to check out how things were made in the original game, you'll get many new ideas.
I would consider changing the name as well, "The Unknown Manor" is quite straightforward. The name is ok, but something else might draw more attention.
I'm not complaining, these are just friendly tips to make your CS better
PS. Maybe tell us a little what the story's about ?