Ikaho Onsen is a hot spring town about 2.5 hours by bus from Tokyo (Buster Shinjuku bus terminal in Shinjuku Station). It’s on the way to the famous Kusatsu Onsen further north in Gunma. Ikaho is a quiet and pleasant hot spring on a cool mountain slope. The hot spring town’s main drag is the famous Stone Steps (Ishidan 石段), an uphill pedestrian stairway lined with shops, restaurants, and inns. There’s also a public hot spring bath (Ishidan-no-Yu 石段の湯) convenient for daytrippers. For wheelchair users, there is an alternate slope up.
Since the 19th century, Ikaho was a popular summer retreat for government and corporate bigwigs, novelists, and other celebrities especially while the Imperial family had a villa there until 1945. One of the dignitaries who had a summer villa in Ikaho was Robert Walker Irwin (1844-1925 ロバート・ウォーカー・アルウィン), the Hawaiian Minister (i.e. ambassador) to Japan in the late 19th century and a prominent businessman with close ties to trading company Mitsui. (Upper right photo is Irwin and wife Iki in middle age.) Irwin and his biracial children spent every summer in Ikaho from 1891 until his death in 1925. A small part of his villa is still preserved in its original location in Ikaho and open to the public (left in the upper left photo).
Irwin is most noted for successfully negotiating and executing the Kanyaku Imin immigration treaty (官約移民) with the Japanese government. This treaty started the mass emigration of Japanese laborers to the Kingdom of Hawaiʻi from 1885. The Japanese laborers worked on sugar cane fields and many of them settled in Hawaiʻi and raised families. The Kanyaku Imin immigration program operated by Japan and Hawaiʻi lasted until 1894, bringing about 29,000 Japanese to the islands. Japanese emigration to Hawaiʻi was then taken over by the private sector, bringing a total of 200,000+ Japanese to Hawaiʻi by 1924 when the U.S. Congress prohibited further immigration. Many Japanese Americans today are their descendants. (I’m not one of them.)
While living and working in Japan from 1866 until his death in 1925, Irwin had a most fascinating life in one of Japan’s most historic periods. He witnessed Japan transforming from a land of samurai into a modern state that shockingly defeated Russia in war and conquered large parts of Asia. He got rich from Japan trading with Western nations, met with both King Kalakaua from the Hawaiian Kingdom and Emperor Meiji, became the first American to legally marry a Japanese national, raised the world’s first American-Japanese biracial children in Japan, and made many high-powered friends in Japanese government and business.
Irwin first came to Japan in 1866 as a young businessman from Philadelphia, Pennsylvania to work for Pacific Mail Steamship Company in Yokohama (the same company that would provide the ships that brought the Japanese immigrants to Hawaiʻi). He was a fifth-generation descendant of Benjamin Franklin through his mother, and his father William was a US diplomat, mayor of Pittsburgh, and Pennsylvania Congressman. Such a privileged family background certainly opened many doors.
Irwin was known to be an affable person and developed close connections with top Japanese government figures such as Ito Hirobumi and Foreign Minister Inouye Kaoru, a key person who decided Japan’s emigration policies. It was most apt for Hawaiʻi’s King Kalakaua to appoint (or promote) Irwin as the Hawaiian Minister to Japan to bring Japanese laborers to Hawaiʻi. Since Hawaiʻi’s native population was declining due to diseases that the white man had brought, Hawaiʻi was in dire need of more people.
Another significant and historic milestone by Irwin was his legal marriage to his Japanese wife Iki. It was the first legal marriage between an American and Japanese national. Irwin and Iki had to wait years until both their governments made it legal for an American and Japanese national to marry. Their children were therefore the world’s first biracial American-Japanese. All of you Americans married to a Japanese national, please note that it was Robert Walker Irwin and his wife Iki who paved the way almost 140 years ago for your marital bliss. 
In the upper left photo, the building on the left is a small part of Irwin’s Ikaho summer villa (Hawaiian Minister’s Ikaho Villa ハワイ王国公使別邸) that has survived. It’s near the bottom of the Stone Steps. The two-story building is open to the public for free. Basically a Japanese-style interior, fully restored and relocated here in 2013. The modern building on the right is a small museum displaying personal effects and letters possessed by the Irwin family. Free admission to both buildings.
The lower right photo shows a Shibayama inlay lacquered tsuitate wooden screen displayed in the Music Room of ʻIolani Palace in Honolulu. The screen shows birds and plum blossoms. It was a gift from Irwin to King Kalakaua when Irwin was on the ship that brought the first Kanyaku Imin immigrants to Honolulu.
In 1997, because of its Irwin connection, Ikaho (now part of Shibukawa city) established sister-city relations with Hilo, Hawaiʻi and started an annual four-day summer hula festival called the Ikaho Merrie Monarch Hawaiian Festival (伊香保ハワイアンフェスティバル). Hula troupes from all over Japan come to Ikaho and dance on multiple stages during the festival. The main attraction is the nightly performance of a top hula hālau (hula troupe) from Hawaiʻi invited to Ikaho. The lower left photo shows an outdoor hula stage on the Stone Steps during the hula festival. Sadly, the festival was canceled in 2020 and 2021 due to the pandemic. Hopefully, it can be held in 2022 onward. 
From the Buster Shinjuku bus terminal at JR Shinjuku Station (near South Exit) in Tokyo, there are JR buses to Ikaho, taking 2.5 hours. Get off at the Ikaho Ishidangai stop (伊香保石段街) at the bottom of the Stone Steps. Day trippers can store luggage in the nearby lockers. Irwin’s villa is a short distance up the Stone Steps on the right side.
More about Irwin: http://www.discovernikkei.org/ja/journal/2020/10/11/robert-irwin-1/
Irwin villa English pamphlet: https://www.city.shibukawa.lg.jp/kankou/midokoro/history/kanrenshisetsu/p000266.html
日本語版: https://www.ikaho-kankou.com/calendar/ikahohawaii2019/
Hula festival: https://www.ikaho-kankou.com/calendar/ikahohawaii2019/