Yoga. It really helps to clear my head and recenter me. What's strange is that the hardest part at first is not necessarily the poses themselves, but rather when you are in a pose like
savasana learning how to clear your head and learning how to focus on your breath in order to keep it clear. It's a skill that once learned is easily transferable to other situations, and that is where it becomes so effective in destressing. Plus, there are a great many poses beyond savasana that take all imaginable effort and focus to hold, and to keep to the right patterns of breath. It brings a whole new level of mindfulness to life that I can't describe unless you try it.