A good place to park is at N47°19.688 E15°21.666 ("P1 Einfahrt")
in Mixnitz. From there cross the "canal" and the road. Look around,
below a stop sign you will find a first signpost showing the way to
Kreuzkogel & Schiffall. Follow them!
Note, that above description may be outdated due to the ongoing
construction work of the nearby S35 motorway.
Shortly before you'll arrive on either summit, the path will
split (towards Kreuzkogel to the right, towards Schiffall to the
left) and the cache is near!
I strongly recommend to visit at least the Kreuzkogel summit
(N47°18.857 E15°20.674). Although its elevation is "only" 1181m it
offers a surprisingly good view. For the last few meters to the
summit add half a star to the terrain rating (see pictures).
The Schiffall summit (N47°18.746 E15°20.371) is slightly higher,
but doesn't offer such a magnificient view, because it is grown
over. But the area looks very mystical, due to the trees clinging
on to the rocks.
If you can, leave another car (or a bicicle) at Laufnitzdorf
(N47°17.507 E15°19.195) and descend there from Schiffall. Of course
you can start your tour also from there. The tour from Mixnitz via
both summits to Laufnitzdorf took us 4,5 hrs including all breaks
(and cache hiding).