Grubigstein offers great views of Zugspitze and Gartnerwand. Instead of coming back to Lermoos, this route goes down to Blindsee. Therefore, it is more suitable on a warm sunny day, when you want to take a dip in the lake after hiking.
Reaching the start point: There are direct trains from Munich to Lermoos, which is the best way to reach the start point. Werdenfels ticket is probably the cheapest option. For the return, one needs to take bus 150 from Fernpass Zugspitzblick to Ehrwald bahnhof, and then take the regional train back to Munich. Note that the bus ride is not included in Werdenfels ticket, and costs approximately 3.8 Euro per person. The bus is also not very frequent, so one needs to plan accordingly. Here is the bus schedule.
Ascent: The route is easy to follow once you locate the start point from Lermoos train station. From Wolfratshauserhuette, there are two options - either a long and flat route via Grubigalm, or a more direct and steeper route (The steeper route is better, and is also the one planned here). The ascent from cable car to the peak requires head for heights, and may also be crowded because a lot of people come to the top using cable car. Vorgipfel seems be to less crowded. At the top one can enjoy the views of Zugspitze and Gartnerwand.
Descent: From the cable car station there is a wide road to Grubigalm, however, one can also take shortcuts. From Grubigalm, the trail is along a forest road, which is also used by bikers, so one has to be careful in this part. The descent is particularly intersting as it offers great views of Blindsee.