We tried to go to the coastal village of Piran but it was mayhem and there wasn't any parking for camping cars so we got the hell out of there and checked out the Postojna caves. It was a bit too crowded for our liking. We managed to keep our distance but once again swore to only go to outside sites (until we forget).
It really was an impressive cave. first opened up when the King of Austria (those Hapsburgs again) came to visit, it has grown since then and is a good trip on a little train and then a very easy walking path. This photo shows spaghetti stalactites which really were amazing but not quite captured in the picture.
The growth rate for stalactites/mites is 1cm for every 100-400 years. One is 16m tall amd estimated to be 150,000 years old.