Iwaki Yumoto Onsen — 1,600-Year-Old Coastal Hot Springs

Iwaki Yumoto Onsen (いわき湯本温泉) is one of Japan's oldest documented hot spring resorts, with written records dating to 556 AD during the Kofun period. The natural sulfur springs emerge at 60°C along the Yunokawa River, flowing at 5.5 tons per minute — among Japan's highest volume hot spring outputs. The water's high sulfur and sodium chloride content creates slippery, beautifying waters (nicknamed 'bijin-no-yu,' 美人の湯, 'beauty hot springs') that leave skin notably soft. The onsen town stretches along the river valley with multiple ryokan, public bathhouses, and footbaths creating a traditional spa town atmosphere just 5km from the Pacific coast.

The area was historically a retreat for feudal lords traveling between Edo (Tokyo) and northern domains. Today, it combines traditional onsen culture with proximity to coastal attractions (Aquamarine Fukushima aquarium, beaches). The most unique experience is Sahakonoyu (さはこの湯), a municipal bathhouse built in traditional sukiya-zukuri style with separate indoor and outdoor baths featuring milky-white sulfur water. The town also hosts the Yumoto Onsen Hula Festival in September, celebrating the local connection to Spa Resort Hawaiians.