I don't want to be a tease about what it is--it's the north pole of Saturn, shot by the Cassini probe in the infrared--but the real question is why it is. Where did that hexagonal shape come from? NASA says "this and other images acquired over a 12-day period between Oct. 30 and Nov. 11, 2006, show that the feature is nearly stationary, and likely is an unusually strong pole-encircling planetary wave that extends deep into the atmosphere." More HERE.
You may recall from earlier images that Cassini is now in an orbit around Saturn that takes it high over both poles, with very striking results (see our slide show HERE), but this is one of the first night polar images to come out.
No, there's no monolith in the center.