Mindolluin or Mount Mindolluin was a mountain in Middle-earth, the easternmost of the White Mountains. Below and to the east of it stood the city of Minas Tirith.
History
Shortly after Aragorn's coronation as King Elessar, Gandalf took him by an ancient path into the foothills of Mindolluin, far above the city. There, upon an otherwise barren slope in a Hallow visited only by the Kings, he discovered a sapling of the White Tree of Gondor, which he planted in the Court of the Fountain.
Etymology
Mindolluin is Sindarin for "towering blue head"; the double "l", as with all double letters in Sindarin, was pronounced as two separate letters rather than one, like the "n" sound in the word "pen-knife".