This is a great viewpoint of Stockholm and definitely a hidden gem.

It's a short little walk up a gravel road and then a few rocks, probably only a quarter of a mile. It's walkable from the subway as well. Once you get to the top, there's a great view looking back to the main island of Stockholm and Gamla Stan. There are also some good views of houses of Södermalm.

You won't find this on many lists of things you should do in Stockholm and it's a little off the beaten path, but it's definitely worth seeing. I highly recommend stopping here while in Stockholm.