Reintal is the easiest or at least one of the easiest routes to hike Zugspitze. It starts in Ehrwald by the Ehrwalder Almbahn (rail). You have an option to take the cable car to the first logical unloading point ~4900 ft, or start exactly by the load point which is roughly 200-250 ft lower.
I will conservatively grade the hike “easy” and climbs roughly 2600 ft to the gatterl (picture this as the point where you switchback to the unseen side of the mountain). The trail is paved soil for the most part.
Above is the view from the “gatterl” post which the trail quickly loses roughly 100 ft (you can see this above as a narrow trail towards the left) before gaining another 1200 ft to hike up to the Sonn-Alpin restaurant. The total elevation gain for this stretch (first cable car stop –> Sonn-Alpin) is therefore ~3700 ft.
Sonn-alpin is another stop to get in and out of the cable car. Most people may like to hike up to the Zugspitze summit and take the cable car on their way down. For that you need to hike up from Sonn-alpin to the summit (passing a patch through the glacier) or take the cable car to the summit. You can then take another cable car, the Tiroler Zugspitzebahn all the way down to the parking lot from where you can take the free bus ride back to the Ehrwalder Almbahn stop. Note the last bus leaves at 5pm but you can always request the nearby hotel to call you a taxi. The entire trail length can be estimated at a little under 6 miles (first cable car stop -> Sonn-Alpin). The entire available stretch (Ehrwalder Almbahm –> Zugspitze Summit) is detailed at 14 kms (~9 miles). The stretch to Sonn-Alpin should take not more than 120 mins to climb up. In comparison the way down through the cable car takes only 10. 🙂 All that time you save…
Notable mentions: The trail dips down immediately after gatterl and climbs back all that elevation through a rocky face of the mountain, and after roughly 5-10 mins into the climb you come across the Austria-Germany border crossing on the mountain.
(Above) Somewhere after the border crossing and before the knorrhütte (hut). Excitingly enough we got caught up in an incessant hail and snow blizzard beyond here, which only started as promised rains. I got no pictures past this point as it was extremely windy (at least 90-100 mph and some stronger gusts knocked us down a few times, yes anxiety worthy). We started the hike on a rocky mountain and on a pleasant sunny day with blue skies and one lost “loner” cloud directly above our heads and ended the hike with a blizzard on an overly-cast snowed-in mountain. They even suspended the cable cars for a period of two hours till the winds subsided in the evening and shut down the entire area for tourists and employees, while opening the last run for people to get off the mountain. Before and after below.