Get to the above site from here:
You can download all the sources of this site, which look like this in SVN:
Go here to see the above: http://svn.hippocms.org/repos/hippo/hippo-demos/hippo-go-green/trunk/
When you open the downloaded sources, you can open the whole app, which is Mavenized, into the IDE, as you can see here:
Then you can explore the sources and really learn how Hippo applications are constructed.