An eminently high place for a flashy warning (6)
I believe the answer is:
beacon
'warning' is the definition.
(I've seen this before)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for beacon that I've seen before include "Directional transmitter" , "Shining light (on top of a hill?)" , "Warning light on hill or cliff" , "Light on a height for navigation or warning" , "Guiding light?" .)