The original DKC trilogy is my favorite collection of gaming soundtracks ever, which the most relaxing ones have already been pointed out numerous times on this thread. So I'm choosing a couple others from the most recent DKC game, Tropical Freeze. They're a bit more upbeat yet still give you a feeling of relaxation. Long live David Wise!!

This or Stickerbush Symphony. Heck, I think I need to go back and do the trilogy again. They are some of my favourites and the music is a huge part of that. 

Took me WAY too long to appreciate the genius of this game. I liked DKCR but it had control issues that ruined it for me. The same can't be said for Tropical Freeze. 

This thread is making me cry. so many beautiful songs. I'd like to add another Dave Wise (**Edit** apparently this was one not done by him, it was Matt Griffin?) song from Yooka-Laylee and the Impossible Lair:

I think I have not seen it mentioned here yet - Minecraft has actually several tracks that I find supremely relaxing. Always puts me in a super chill, zen-like mood.