The calendar-stone is situated at the edge of the little village Leodagger. Leave your vehicle near the church and you will easily find the sign-posts (please use the official path around the meadow and the fences) and a board with some explanations.
The following information can be found in more detail in "Urgeschichtswanderweg: Eggenburg-Pulkau-Retz-Znaim by Herbert u. Herta Puschnik". In the area of Leodagger and especially around the calendar stone many artefacts from the Bronze Age have been found. The calendar stone is a large granite boulder of about 4m height and 8m length. Its sides are orientated almost exactly north/south and east/west. Next to the southern wall a separated granite pillar rises. Through the crack between this pillar and the rock it is possible to look eastward or westward. This crack might have been used to watch the sunrise and sunset at the time of the equinox in spring.
On top of the boulder, on the western side, there is a row (running from north to south) of 16 tiny little bowls. The photo in the book shows more bowls than can be seen on a sunny day now (sometimes they are made more visible by chalk, I don't know who does this). On the way up to the top there are two larger bowls, but there is no proof that anything of these two bowls has been made by humans.
The cache is only a micro (plastic tube) with a small logbook and a pencil. Have a look at the hint and the spoiler-picture BEFORE you start taking the rock apart or exploring the thorn-bushes (at the time the mentioned book was written the area seemed to be much less overgrown).
Happy Caching!