Hallein Saltmine outside of Salzburg, Austria. One of the highlights of my first trip to Europe as an 11 year old. You get to ride down huge banister like slides, take a little boat across an underground lake.
Königstein Fortress (Festung Königstein), the "Saxon Bastille", is a hilltop fortress near Dresden, in Saxon Switzerland, Germany, above the town of Königstein on the left bank of the River Elbe. It is one of the largest hilltop fortifications in Europe. The fortress, which for centuries was used as a state prison, is still intact and is now one of Saxony's foremost tourist attractions.