I have been doing Wim Hof's breathing exercises for years now, nost often first thing in the morning as a kind of meditation and energiser. It seems to waken up both body and brain.
I sometimes use it before something I'm a bit nervous about (injections in my eye) or before a social occasion I am stressing about (recent funeral). I find it deeply calming, and of course you need no equipment or special clothing and can discreetly do it anywhere.
It's exercise I can honestly say I enjoy!