A nice destination run is to run along the shore of the Starnberger See (Lake), the second largest lake in Bavaria. About 30 minutes south of Munich on the S-Bahn (train), it’s a great opportunity to get out of the city and enjoy an alpine lake in an easy and continuous path. The eastern side of the lake is more recommended for running, with a 20km long shore side path from north to south. Run as long as you like of course. The town of Leoni is a good destination, at the ~7km mark. There is a steep hill at the 5km mark. Along the way, there are beaches, parks, and a couple of sections with spectacular homes. There are a couple of detours off the main lake path, such as around the Castle Berg, but it is well marked.
One could continue further along past Leoni, and hop a ferry back to Starnberg. It’s another 6km from Leoni to the next town, Ammerland. On the west side there are additional S-Bahn stops along the lake. See this guide for Lake Stanrnberg sites, ferry schedules, and other info.