'Caves of Forgotten Dreams' (2010)
You could argue that a huge portion of Herzog's filmography, even his fictional entries, might qualify as "nature documentaries" in a broad sense; even something like 1992's Lessons of Darkness, a narration-less, season-in-hell portrait of Kuwaiti's burning oil fields, technically fits the category. This journey into France's Chauvet Caves, home to paintings carbon-dated at 37,000 years old, is as close to a straightforward feature-length nature doc he's made – and it's one of the few movies shot in 3-D (a process Herzog had long dismissed as ridiculous) that takes complete advantage of the format. It's filled with unbelievably beautiful imagery, a staggering number of the director's parody-ready voiceover nuggets ('It is as if the modern human soul had awakened here") and a singular philosophical perspective on the orbiting rock we all live on. It's truly unforgettable.