Archaeology & Mysteries - 5 free documentaries about ancient engineering.
Start with 3+ Hours Of Unexplained Ancient Mystical Artifacts (195 min, Odyssey), then Mystic Energy Lines Run Through New York? (21 min, HISTORY). All 5 documentaries here are free to watch from their makers' official uploads. To read deeper, the top-rated book on ancient engineering is Decoding the Heavens by Jo Marchant.