If you find yourself in Koriyama, either changing trains or staying for a night or two, then a decent place to fill an hour is Big I. It's a striking 24-storey skyscraper, comfortably the tallest building in the city at a cool 133 meters, with a couple of reasons to visit.
The first five floors are a shopping center called Molti, four floors of shops and one of restaurants. Each shopping floor is on a different, helpfully broad theme: 'Foods and Variety' on the first floor includes The Body Shop and 7-11; 'Fashion and Cafe' on the second has Starbucks surrounded by womens' clothing stores like Mix-O and Arise Gate; the third is 'Young Casual', mostly also womens' clothing stores, among them Trice and Amare MylePR; and on the fourth, the catchall 'Goods' theme covers flower design, order made curtains, and employment service Hello Work.
The fifth floor is 'Restaurant and Service', with more of the former than the latter. There's a nail salon and a fancy-looking hair salon, and a handful of restaurants and cafes; I had a light, pleasant salad lunch at La Maison ensoleille, but you can also have Chinese or Italian food, shabu-shabu at the Japanese restaurants, or snacks or pancakes at the cafes.
Much of the rest of the building is commercial, but when you get up to the 22nd floor, things get interesting again. Here there's an observation lounge with excellent views over the city and encircling mountains, and you're actually walking round the Fureai Center "Space Park", an astronomy museum aimed mainly at kids. This includes a planetarium which is evidently the highest in the world, at 104.25 meters elevation, though I don't know how much competition there is for that particular record.