Atlas of geographical curiosities

The world is full of very little-known geographical anomalies that are or have often been a source of diplomatic and/or military struggles. Many still exist under the radar and are, or could become, the source of a major international crisis.
Countries that do not really exist, the world's only town that lies entirely underground, a UK hotel room that became Yugoslavian for one day only, an island which is Spanish for six months of the year and French for the other six months, a city which is officially constituted by one single skyscraper, the world's first and only railway that belonged to one country and ran across another, a hotel room whose bedroom is in France and whose bathroom is in Switzerland, Bir Tawil which is one of the very few territories on Earth not claimed by any country, the only place in the world where you can find the so-called counter-enclaves and where in a 20-minute walk around the village you can cross an international border over 50 times at 50 different points...