Cache at the summit of the Brünnstein.
There are many possible routes to come here, but the most popular one is from the parking near the Tatzelwurm waterfall via the Brünnsteinhaus. The final ascent to the summit from there can either be done via an easy Klettersteig or via an even easier trail further west (but even that one features some rocky terrain and is secured with some steel ropes).
Overall, the tour is not particularly hard, but of course some general fitness, secure footing, proper mountain equipment, etc. are nonetheless needed.
Numerous tour descriptions can be found online. Please check a few of them for more details.
You do this cache at your own risk! It is your own responsibility to decide whether your abilities suffice to do this cache!