Dol Guldur
Gandalf suspected early on that an evil presence, the Necromancer of Dol Guldur, was not a Nazgûl but Sauron himself. He went to Dol Guldur to discover the truth, but the Necromancer withdrew before him. The Necromancer returned to Dol Guldur with greater force, and the White Council was formed in response. Galadriel had hoped Gandalf would lead the Council, but he refused, declining to be bound by any but the Valar who had sent him. Saruman was chosen instead, as the most knowledgeable about Sauron's work in the Second Age.