I swallow rivers, vast and deep, My layered walls, ancient secrets keep. What am I, where echoes sleep?

From medieval fears to farmers’ woes, my shadow falls wherever it goes.

Where iron binds and hope wears thin, a place where few escape once in.

A sailing ship, used for war and trading, remove an e and I'm a unit of liquid capacity.

A song by Yes. Add an s for a book by RAH, a movie trilogy or a video game. The first word is what Jefferson Airplane became, the second is what your boss says you are if you come in on the weekend to help solve the problem he created