Synonyms: weird, eerie, uncanny, unearthly
These adjectives refer to what is of a mysteriously strange, usually frightening nature. Weird may suggest the operation of supernatural influences, or merely the odd or unusual: "Nameless voices—weird sounds that awake in a Southern forest at twilight's approach,—were crying a sinister welcome to the settling gloom" (Kate Chopin). "The platypus ... seemed so weird when first discovered that a specimen sent to a museum was thought to be a hoax: bits of mammal and bits of bird stitched together" (Richard Dawkins).
Something eerie inspires fear or uneasiness and implies a sinister influence: "His white countenance was rendered eerie by the redness of the sagging lids below his eyes" (John Updike).
Uncanny refers to what is impossible to explain or accept: "My mother had an uncanny ability to see right through to my motives. At the time I wondered if she had ESP" (Porter Shreve).
Something unearthly seems so strange and unnatural as to come from or belong to another world: "The joy of having escaped death made the unearthly ruins of Hamburg seem more like a smoldering paradise than the purgatory other people thought our once lovely city had become" (Marione Ingram).