[Zigûr]

He might be referring to the ruins of Fornost, which were near Bree and referred to as "Deadmen's Dike" by the Bree-landers in reference to its disastrous fall during the wars with Angmar, although whether or not Fornost was genuinely full of evil things might be less certain. The Rangers still visited it, so perhaps not. He might be just generally referring to the evil things which had dwelt in Eriador since those days - Orcs, Trolls, Wolves and the like roaming the wilderness and waylaying travellers.