There are several bridges that connect the two islands together, as well as to the rest of the city.
Of course, the Notre Dame Cathedral is here, which is the focal point of the Île de la Cité. You'll see you're there when you see the long queues and the shady Gypsies trying to scam you with their tricks.
At the eastern tip of Île de la Cité, there is the Mémorial des Martyrs de la Déportation, commemorating the victims of the Nazis during the Second World War in Vichy France. Unfortunately, it was closed when we visited, due to recovery efforts from floods that occurred a few months ago when the Seine overflowed its banks. And at the western tip of Île de la Cité is Pont Neuf, or New Bridge, which is actually the oldest bridge across the Seine, built from 1578 to 1607. My photos above show you this bridge, which in my opinion, is quite nice to look at.