Long but fairly easy hike.
From the summit, you can enjoy the nice view of almost all peaks in Chiemgau alps.
Reaching the start point: It would be ideal to go there by car, as public transport options are not very reasonable (Requires one train ans two bus rides as described in next section). One possibility is to take the shuttle bus to Hindenburghuette, and start the hike from there. Please check the website if you want to use that option.
Ascent: The route is very long, but mostly on the mountain roads, which are not too steep. One thing to consider is that many signposts along the route only show the huts, and not the peak Fellhorn, so just believe at the gpx track and follow it.
The steep part starts at Straubingerhaus, and once you reach the saddle point, the peak is already visible. After a couple of ups and downs, the peak can be reached from there.
Descent: Almost the same as ascent except a detour near the top, This detour could be useful as it passes through Hindenburghuette, which is open during winters, while Straubingerhaus is not.