Stuttgart 21 is a long planned (10+ years), hotly debated (100+ police arrests and dozens of canisters of teargas, some of them used against elementary school students) improvement project to the German Railways (Deutsche Bahn), comprising 2 big pieces.
The first piece is a high speed rail line between Stuttgart and the very-large-but-still-too-far-for-easy-rail-commuting city of Ulm. Here’s a snap of a railroad viaduct leading to a mountain tunnel, towering above the village of Wiesenstieg,
And the second piece is transforming the Stuttgart main train station (Stuttgart Hauptbahnhof) into a massive underground shopping center,
For the record, I originally opposed this project when I first learned about it in 1998, for one reason alone: compared to all the other public toilets at train stations, the public toilets at the Stuttgart Hauptbahnhof were and still are today atrocious. For a culture in Germany known for its tidiness (e.g. Kehrwoche), if you can’t trust them to operate a toilet correctly, how could you trust them for a project this big?