Internal or external feed? That URL is just not right.
To get an internal RSS feed of a section:
If you wish to build your own feeds (internal) to show within the main RSS link in the bottom left, you can do this from your ACP in the following location
System -> Content Discovery -> RSS Feeds
When creating a new feed, you can choose which sections you wish to 'feed' into this new RSS feed. Here we have created a feed named 'Test Feed', which shows information only from a specific calendar.