Wow, soti, nice pictures! Thank you for sharing. Wouldn't want to bike there though, doesn't look the least bit safe...
I suppose the usual suspects already know the location of the tag, but a little interesting info might still help those who don't.
This relatively young specimen (it's only slightly over a hundred years old!) was planted in honour of a beloved emperor on behalf of the field marshall Radetzky.
Nowadays it is still an important piece of our cultural heritage. Have a look at the two cent coins in your wallet. Our neighbours to the north used oak leaves on the Deutsche mark, before our current popular currency.
The tree, however, has been a highly esteemed one for many thousands of years. The republican romans awarded crowns of oak leaves for those who saved a life in battle. A symbol of wisdom and strength, it was essential to the druids, as well as to the first cultures of the American continents. You will find this powerful tree in the centre of many European mythologies.
It is renowned for its healing powers (location!), and is said to be a source of energy. It is said that if you catch a falling oak leaf, you shall have no colds all winter. Find an acorn, and keep it! It will ward off illness and pain, and help you keep your youth.
So, by all means, when you find the tag, stay a while, and remember to give it a nice big hug! (it's circumference needs slightly more than three of me to hug it though ;-)