Nago was founded on 1 August 1970 and has about 60,000 people with an area of about 210 km².
From Naha bus terminal (across the street from Asahibashi monorail station) you can take the Expressway Route bus No. 111. The trip will take about 2 hours and will cost ¥2,040. There will be many stops along the expressway on route. The No. 111 runs all the way from the Naha airport as well and costs ¥2,160.
It is easier and less expensive to take a tour with a private company which typically includes admission to the aquarium along with other side journeys for 5000￥ compared to 5600￥ just for transport plus 1800￥ for admission to the aquarium. The ride is also shorter as you do not have to make stops for passengers although there are of course stops for other attractions depending on your tour. The tours typically allow you 3 to 3 and a half hours at the aquarium. They begin around 8 am and finish around 6pm, depending on the tour. http://okinawa.0152.jp runs tours if you would like more information. A Japanese speaking guide is also provided. Generally no English.
The park of the Nago castle is on the Top 100 list of cherry tree flower viewing (hanami) spots of Japan, and the only place in the Okinawa prefecture on the list.