My roommate recently moved out of my house so now it is just me and my dog.  My dog is really nice and doesn't really bark unless he sees a stranger coming up to the house.  Lately he has been sitting at the top of the steps to the basement and growls/barks.  However, there are no windows to the basement and he wouldnt be able to see into the basement.  I have no idea why he has been barking at that door lately.
I'm not bothered by him barking.  As someone who watches a lot of scary movies it is more of a worry factor that someone is down there than anything.