They do have a nice zoo and a small water park called Raging Rivers just across the river in Mandan. Might want to check that out? Also lots of bike, walking, and in-line skating pave trails in all the parks that line the Missouri river in Bismarck. You can pretty much bike, walk or skate for 5 miles or more in nicely treed parks and river views. You will see lots of young people hanging out in the parks and on the trails as well.
http://bisparks.org/parks-trails/park-trail-maps/
Raging Rivers WaterPark | Mandan, ND
If you are into golf...there are plenty of courses in the Bismarck Mandan area as well. 5 in Bismarck and 2 in Mandan.
http://www.golflink.com/golf-courses...st=bismarck+nd
If your into history, check out the North Dakota Heritage Center on the capitol grounds and also fort Lincoln (Custer house) over in Mandan.
http://www.parkrec.nd.gov/parks/falsp/falsp.html
http://www.history.nd.gov/ appears the Heritage Center is closed due to construction and additions, but the Capital Building is worth checking out...observation deck on the upper floors for some good shots of the Bismarck-Mandan area from above.