Burgstall / Monte Castello and the Roßzahn Ridge. Touristensteig negotiates the slopes behind the summit
Even though it is a valid route to Petz / Monte Pez, the summit of Schlern / Sciliar, Touristensteig (literally "tourist trail") wouldn't be worthwhile a thorough description. "Take the cablecar from Seis / Siusi, then follow the masses" would suffice. Maybe a warning about elevation gain (=1000m) and footwear would be a good idea. But if you want to skip the cablecar and start from Seis / Siusi directly, things turn different.
For one thing there are several options for the first leg of the trip. The one described here uses Oswald von Wolkenstein Weg, a picturesque hiking trail beneath Santner- and Euringerspitze, which touches upon two medieval castle ruins before reaching the path to Schlernbödelehütte. The overall elevation gain runs up to more than 1650m, turning the whole trip (one way) into a 4h affair if you're quick. An early start is advisable so that you don't have to go with the crowds on the last leg, Touristensteig.
Seis / Siusi seen from Salegg Castle
Seis / Siusi can be very easily reached. Just take the Brenner Motoorway A22 to the exit Waidbruck / Ponte Gardena, then turn onto SP24 to Kastelruth / Castelrotto and Seis / Siusi.
Panorama Seiser Alm from upper Touristensteig
Start altitude: 1020m
Summit altitude: 2563m
Prevailing exposure: N
Effort: 5 - 1650m elevation gain
Power: 4 - Long and strenuous
Psyche: 1 - No exposed sections
Difficulty: 1 - Steep ascent
Orientation: 1 - Marked and easy.
From the centre of Seis / Siusi follow the main road (SP24) southward heading for the big parking lot of the cablecar. Pass it, following signs to Hotel Salegg, a large building outside the village limits. Here Oscar von Wolkenstein Weg actually starts by leaving the road and heading up into the woods beneath Santnerspitze / Punta Santner. After three switchbacks you'll reach the ruins of Salegg Castle, of which little more than a few walls remain upstanding. The forest has been cut around the ruin so that you have some wonderful views across the village.
Return to the path through the woods, which will lead you to the similar positioned ruins of Hauenstein Castle. Here more walls, trenches and ramparts remain in place so that you get a much better feel for the castle behind the ruins than at Salegg. In particular you can have fine views of Santnerspitze / Punta Santner rising directly above the castle.
Returning to Oswald von Wolkensteinweg you soon get the the Hotel / Spa at Bad Ratzes, also an option for a trailhead as it can be reached by car and has a large parking lot. The road, however, ends shortly after the hotel and a well worn footpath leads you in direction of Seiser Alm / Alpe di Siusi. After 700m on this path you get to an intersection where an upturned tree serves as the gate for the next leg of the trip, the so-called Geologensteig (named after the geology signs, that have been put up along the trail.
Coincidentally this is also the trail to Schlernbödelehütte, one of the many huts which cater to thirsty hikers on Seiser Alm / Alpe di Siusi. The path heads up steeply in many switchbacks to an elevation of around 1700m, where it reaches the hut. Close to Schlernbödelehütte there is an intersecttion with Gamssteig, a more direct but seriously exposed route, which cuts short the lower sections of Touristensteig, with which it recombines on the Schlern / Sciliar Plateau.
Stay on the main path, however, which mor gradually ascends towards Seiser Alm / Alpe di Siusi in a long bend. Several trails, after having crossed the pasture join our trail and it is here that it turns into the last leg of our trip, Touristensteig (at around 1900m). It turns real steep, still crossing the pasture, later cutting steeply through the undergroowth of dwarf pines. From heavy usage Touristensteig is deeply rutted and thus more strenuous than one would expect. It cuts through the north face of Schlern / Sciliar where it is weakest, but still rather steep. Numerous switchbacks take you acrosss the timberline at 2200m. A longer traverse takes you to the exit onto the plateau, soon after which the aforementioned Gamssteig rejoins. From here it is a mere stroll to Schlernhäuser / Rifugio Bolzano and the remaining 100m ascent to Petz / Monte Pez. If yoou still have power inside yourself you can hike northwards to the Burgstall / Monte Castello Summit or even onward to the Kanzele / Pulpito outlook above the Santner and Euringer Towers.