Frognerseteren is a very small village and restaurant at the eastern end of the blue T-bane line (Line 1). There isn't much there in the summer apart from the restaurant, gorgeous wildflowers, and wonderful views of Oslo and the Oslo fjord.

It is a good starting point for walks. You can get off at the end of the line and start to walk back down into Oslo, getting back on the T-bane if you get tired.