is due to blood rushing up your brain

eh which onsen at arima is open for visitor ah?
i know some is not open...dk how to ask leh my japanese not that good
You can simply walk in to their public onsen. 2 main public onsens in Arima is Kin no yu and Gin no yu. They are named after the color of their onsen water. Gin no yu is closed till this summer. If u go after autumn it should be open, but need to check first.
Entrance are 650 and 550 respectively. Towels rental charged separately, so bring along your towel, no need those huge one, just one small face towel will do. I used that kind for "modesty" and drying up after onsen. The Kin no yu is just 2 small pools, but the water is brownish(Arima folks prefer to call it golden color

). Though color looked weird but its very smooth to the skin. Something like a very diluted moisturizer.
They are prominently listed in their tourist directory or simply ask anyone they can direct you liao.