It can't be seen, can't be felt, can't be heard and can't be smelt. It lies behind stars and under hills, and empty holes it fills. It comes first and follows after, ends life and kills laughter. What is it?
Two sisters we are, one is dark and one is fair,
In twin towers dwelling we're quite the pair,
One from land and one from the sea,
Tell us truly, who are we?
My first letter is in sea but not in ocean,
The second is in change but not in motion.
My third letter in boat but never in ship,
And the fourth is in travel as well as in trip.
The fifth letter is in dark but not in caves,
And my whole is a triangle popping up from the waves.
What am I?