Recently I have found out that a nuclear plant in my country called the Ignalina Nuclear Power Plant is the most powerful nuclear plant in the world and has the biggest nuclear reactors in the world. Currently it's being closed.
There is a massive fortress complex in my city called the Kaunas Fortress which was constructed in 1882 by Russia for the World War I. More accurately most of it is underground bunkers. There are main strongholds and most of them were connected by underground tunnels. The complex then covered about 65 square kilometers. Currently the connections between the strongholds are blocked. And there are few strongholds less than kilometer away from where I live. One of them is the Ninth Fort and currently there is a working museum in it. With a guide you can get in the tunnels.
The Ninth Fort
The strange buildings you can see in the background are massive 32 meter tall monuments which are memorial to the 30,000 Jews and others from Lithuania and abroad who were brutally murdered here during the Holocaust.