The Skyview Temple theme is pretty relaxing, but I'll have to go with the past theme of the Lanayru Mining Facility. It's so...active and mechanical-ish sounding, but at the same time it sounds kind of ancient. Perfect fit!
I honestly love the Skyview Temple's music because it is just so relaxing. I like the Ancient Cistern for its creepy feeling in its theme. I also like the music in the first Tire Temple. That theme always gave me goosebumps in a good way. I just wished they made an Ice Temple.