The plot, like I said, is basic. A guy who's wife is pregnant gets a call from an old friend asking if he wants to go camping. The old friend - does everyone know someone like this? I feel like this guy is a universal character - is a kind of aged hippy, a guy who sort of hasn't found his place in the world, and basically kind of cruises around looking for meaningful experiences. So they set out on this trip to check out some hot springs. And then they come back. Nothing major or revelatory, but nonetheless, there's so much packed into that trip. It's the best kind of realism: thoroughly probable and persuasive, and yet, honed to a kind of universal profundity, where its as though you can see all the contours of how the world works within it.
Actually, I don't want to say anything else about it, because I think each viewer should draw their own conclusions about the interactions between these two guys - no doubt, the way you understand them will be strongly formed by your own life experiences, more so than is usual in movies - and just say that I highly recommend this movie.