Identify Black Spiders on Cape Cod?

I'm staying in a cottage near a pond in Chatham. Its a fairly wooded area. I have seen two spiders inside the cottage...one was pretty small, one was a bit larger, maybe penny sized, that seem to be all black. One was in the bathtub and one scurrying across the ceiling. They seem a bit thicker than most spiders since they are VERY black looking and very EASY to see. (as opposed to cellar spiders) Can you please help me identify them and tell me if they are dangerous.