Crater Lake is a lake in a caldera.  In the middle of the lake is an island that was formed as the eruptions from beneath built up a new outcrop from the original caldera.  That island has itself formed a caldera on the summit.  The scale of everything is so large that it is easy to not even notice that this second caldera sits within the first caldera.  There are some trees on the island that give you some context as to how large it all is.