Tokyo (Ueno Station) and Iwaki (Yumoto and Iwaki stations) are connected by hourly Super Hitachi limited express trains along the JR Joban Line (2 hours, around 6000 yen). The trip is fully covered by the Japan Rail Pass, JR East Tohoku Area Pass and JR East South Hokkaido Pass. Note that Yumoto Station is closer to most of the city's tourist attractions than Iwaki Station in the city center.
Getting to Iwaki from Tokyo
Multiple bus companies operate hourly highway buses between Tokyo Station and Iwaki Station (3 hours, 3800 yen). Instead of using Iwaki Station, it can be more convenient to get off at the Iwaki Yumoto IC bus stop (160 minutes, 3600 yen), not far from the Spa Resort Hawaiians, from where infrequent local buses provide transportation to Yumoto Station and the spa resort.
Above fees and schedules are subject to change. Be sure to check current yen exchange rates.
Most of the attractions in Iwaki are located near Yumoto Station and the Onahama (小名浜) port area, rather than in the city center around Iwaki Station. Some attractions are located within walking distance of Yumoto Station, while Spa Resort Hawaiians is accessible from the station by local buses or free shuttle bus. Local buses run between the Onahama area and both Yumoto and Izumi stations.
An alternative would be to tour the city by rental car, which can be convenient considering that some of the attractions are accessible only by infrequent local buses. Car rental outlets can be found close to Iwaki and Izumi stations.