The single word that you would use is striking.
That strikes the attention of an observer; producing a vivid impression on the mind; telling, impressive, unusually remarkable. [OED]
People in red satin evening gowns, the pyramids in Egypt, and platform heels with fish in them are also striking. [vocabulary.com]
There is also the idiom not believe one's eyes that you can consider.
Fig. not to believe what one is seeing; to be shocked or dumbfounded at what one is seeing.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs
Example:
When we arrived, I couldn't believe my eyes. Picture it – pyramids – gigantic pyramids of stone stretching into the heavens surrounded on all sides by miles and miles of bleach white sand.
The Hands of Aldulan - Book Two: The Isle of Dusk By Eric A. Radulski
There is also the ear version: not believe one's ears.
