Technically not challenging, but the ascent requires good orientation skills, which will be rewarded by the views of Plansee and Ammergau alps during descent.

Reaching the start point: There are regional trains from Munich to Reutte (not very frequent though). The start point is Reutte in Tirol schulzentrum, which is the second last stop. The cheapest ticket is Werdenfels ticket, however that also puts some restrictions, as a journey via Kempten will not be an option with this ticket. The route ends at Heiterwang Plansee, which is one of the train stations on the way between Munich and Reutte.

Ascent: After walking a bit along the rails, we turn left and continue on a wide path. One needs to keep looking at the gpx here, because there are a couple of places where we need to exit from the wide path. Finally after descending a bit and crossing a power plant, we reach Stuibenfalle Archbach.

There are two paths here - the right one goes along the klamm, while the left one goes up. We take the left path and start ascending. After the initial ascent the path becomes flat, we continue along the flat for a bit, and then exit from the left to go up. This exit is not visible at all, and one needs to rely on the gpx. There is no path, but there are some faint trails of footsteps. After ascending for 20-30 meters and going a bit right, we reach a wide path again. We continue along it until it reaches an asphalt road.

Here, instead of taking the asphalt road, we continue straight along the steep forest. The path is not maintained, and is hard to locate, but there are red-white marks at regular intervals. Keep following these marks, until we reach the ridge. From here the path is always along the ridge, and is not very hard to find. There are places where we have Latschen trees on the path, and we have to cross them. However, the path is never exposed or technical otherwise. After Schelleskopf the path becomes a marked T2 trail, and is easy to follow all the way to Hochjoch, where we have a small female sculpture guarding a very small cross.

Descent: From Hochjoch to Schelleskopf, we follow the same path as ascent. Then, we take a left turn and descent to the lake along a very well marked trail. This is the most scenic part of the route with views of Plansee and Ammergau alps. After descending to the lake, we walk along it for 1.5 hours to reach the train station.

Variants:

1) In case you don't enjoy hiking along unmaintained and not so easy to find path, you take the same path as descent to go up. 

2) It is also possible to continue after Hochjoch to Soldatenkopfe and further, and then descent from there to lake.