Sendai's Amusement Park: Benyland
Benyland doesn't have a lot, but I really like Top Spin rides so I went on that a few times. Honestly, I can't find a reason to return, but for amusement park fans or those in the Sendai area looking for something fun for the kids, it's a decent half-day stop. There's a zoo next door which would combine for a nice day off.
Benyland is open 9:00-17:00 (until 16:30 in November) everyday from about the second week of March to the last week of November; it opens on most weekends through the New Year, then closing for about two months in January and February.
Admission is 800 yen for adults, 400 yen for kids; all-you-can-ride Free Passes are 3500/3100 yen respectively. Individual rides are 100-500 yen each. Access is easy by bus from Sendai Station; ask for details at the tourist center. You'll probably be headed to Bus Stop 12 to catch a number 9 or 11 bus.