Dristner (also known locally as Tristner) is an impressive mountain. It's north flank is impressively craggy, but it's beauty comes from the great height with which it looms over Mayrhofen. To begin the climb from the outskirts of town involves an elevation gain of over 2000 meters! And yet, given sufficient experience, it is surprisingly friendly -- accessible to a hiker with a head for exposure in the upper 700 or so meters, either from north or south.
On my own climb from the south side beginning in Ginzling, I was warned of the danger when the slopes are wet. From the south, it appears almost entirely as a grass mountain, with 700 meters above timberline very steep and exacting. I shuddered to imagine being there when the grass is slick. The trail, such as it is, is only imprints made by feet, and the spectacular narrow ridge at the end requires some use of hands.
Ginzling is the ideal starting point. To reach it travel the A12 from Innsbruck or from Kufstein, then follow the 169 at signs to Zillertal and Mayrhofen. Pass Mayrhofen, then make a left (still on 169) at Finkenberg, following signs for Ginzling. There is a tunnel and a valley-road option (presumably the valley-road is closed in winter). In either case, reach Ginzling where a decently-sized parking lot awaits.
There is a little "Klettergarten" right in town with signs for a via ferrata. Another sign advertises the way to Wandegg with a travel time of 2 hours. Follow this path.
RouteSouthwest Ridge (from Ginzling): As described in "Getting There," follow the path to Wandegg on a steep but pleasant forest path. After 400 meters elevation gain, you'll reach an open area with a few abandoned houses. Soon, deep forest is regained, and after another 500 meters elevation gain, you'll reach a private hut (~1780 meters).
I presume this is the Wandegg? It's hard to know. There are not many signs. There is a spring at the hut with water, though it's on private property (within the fenced area). In general, there are no streams along the route at all, so you should bring 2 liters of water and start early.
One option for water which I haven't tried is that about 120 meters above the private hut, there is a spur trail leading east into the Wandeggkar (~1900 meters). From the sound of it, there should be good water in there until late summer, though it's likely a 15+ minute detour.
Steep, open and flowery meadows lead to the forming crest of the ridge at about 2200 meters. Follow trail up the increasingly well-defined ridge all the way to the summit at 2767 meters. Very exposed UIAA Grade I+. There is a real sense for a long time that a slip would be punished severely. But this just makes the country all the more impressive.
It's over 1700 meters elevation gain from town...with no certain water along the way (short of permission from the Wandegg Hut Owner) -- rather interesting!
North Ridge aka Harpfnergrat (from Mayrhofen): I can't describe this adequately, though it appears a good trail leads from Hochstegen (642 m) up the North Ridge past Harpfner to a point at 1974 meters elevation and the end of forested terrain. From here the ridge can be followed to the summit with considerable exposure (grade I+).