There are three things I find mesmerizing and soothing but only entail watching. These are storms, the sea and fire.
It is so hot here I won't even mention fire again. Only the thought of it makes my brain steam. But it is something I could sit gazing at it for hours on end. The same goes for the sea, which I'll spend hours watching and never feel bored. There is something very relaxing about hearing the waves come and go and the sound of seagulls circling above. Even the cries of children running and playing on the beach makes me feel calm.
And as for storms, I find they're like books. They build up slowly, putting pressure on the characters and showing a grey scenario while anticipating excitement and the burst of thunder. Then, when the downpour comes and washes away all the negative emotions and the overload in the atmosphere, and lightning lights up the way for the characters, peace finally comes leaving happiness in its wake.
What do you find relaxing?