Please make your own hotel arrangements.
Near Wako-shi station (15 min walk from RIKEN)
Please visit on of the following the web pages.
Wakoshi Tobu Hotel:
https://www.tobuhotel.co.jp/wako/en/index.html
Toyoko Inn Wako-shi Ekimae:
https://www.toyoko-inn.com/eng/search/detail/00090/
SUPER HOTEL Wakoshi Station:
https://www.superhoteljapan.com/en/s-hotels/wako/