The Abyss (1989)

The Abyss is very high concept, but to be honest it's a bit dull in places. A deep-sea drilling crew gets pulled into the recovery of a sunken submarine, and finds something unexpected down in the dark. The underwater filming is remarkable, and there's one genuinely great bit of science: breathing liquid is real! Oxygen-rich fluids can be breathed by mammals, strange as that sounds. The alien side of the story is much more far-fetched, and the ending won't work for everyone. Worth seeing, but hard going at times.