Ehrentempel (Munich)

 Second World War 1939-1945, ruins, demolished

The Ehrentempel ("honor temples") were two structures in Munich, erected by the Nazis in 1935, housing the sacrophagi of the sixteen members of the party who had been killed in the failed Beer hall putsch. On January 9, 1947 the main architectural features of the temples were destroyed as part of denazification.
However foundations remain and likely won't ever be erased because a rare and possibly-unique species was discovered living in the ruin's mini-environment. The rainwater that collected there over time created a micro-habitat --a biotope-- perfect a particular kind of vegetation. The presence of the unusual species derailed post-unification plans to erase all traces of the ruin and put up a biergarten on the site.