First of all, no it's not "The Abyss" or "Mission to Mars" (unless I'm really remembering that one wrongly.)
I can only remember what I'm pretty sure is the ending. Wherein a man in a spacesuit walks to a monolithic structure with a dark backdrop. When inside he talks with a female alien I think (she might have been in a dress.) He is then placed inside a tube, without his suit, that has the breathable liquid and shot through said tube that forms as it goes along.
Possibly 70s, think it was grainy, not quite sure. But I will say I'm trying to remember a movie I watched as a kid around two decades ago.