Onsen tamago is a hot spring egg． This is a souvenir of Izaka Onsen．
The onsen eggs of Iizaka hot springs in Fukushima City, Fukushima Prefecture are called radium eggs as it is the first onsen in Japan at which the presence of radium was detected in the water
Because it is difficult to make it, hot spring Tamago recommends that I buy iｔ．
