Keep an eye out at Nakaminato Fish Market — you're sure to come across some unique curio in one of its many stalls. After you've had a thorough browse of things, enjoy a meal from one of the nearby food vendors.
You'll be spoiled for sightseeing choice when visiting Hitachinaka. Nakaminato Fish Market is a great place to start here, but there are loads of other fine attractions to appreciate. Hitachi Seaside Park, Aqua World Ibaraki Oarai Aquarium, and Oarai Isosaki Shrine are close to the community marketplace and and will cap off your day nicely.