Built in the 1980s, Le Formentor is a 27-floor modernist tower in Monaco. Home to tennis star Novak Djokovic, it lies on the Avenue Princesse Grace, one of the most expensive streets in the principality, and thus, the world. It is from an apartment at this iconic address that Riverdance star Michael Flatley is fighting for the future of another landmark building, his mansion at Castlehyde in Co Cork, a protected structure and the ancestral home of Ireland’s first president Douglas Hyde. The entertainer bought the 18th-century mansion near Fermoy in 2001 after he reportedly saw it from a helicopter…