Shirahama Onsen, along with Arima Onsen and Dogo Onsen, is one of the three oldest hot springs in Japan.
The public open air bath of "Saki no Yu" which located right in front of the Pacific Ocean, is particualry popular with tourists.
The flowing hot spring with its mild sulfur smell and saline hot water typically satisfies even the high-level hot spring connoisseur.
Bathing while watching the waves break on the rocks will leave you feeling soothed and refreshed.
You should have an amazing time in "Saki no Yu"!