Our first stop was the Hannibal Visitors Center, where we picked up maps and brochures. Next, we stopped for free ice cream at the Dutch Country General Store. We also browsed their large selection of toys and puzzles.
From there we walked two blocks north, where we climbed 244 steps to the Mark Twain Lighthouse. Look for the statues of Tom Sawyer and Huckleberry Finn and the steps will be on your left. You can't go inside the lighthouse, but my kids enjoyed climbing the steps and there's great views of the Mississippi River.
Our final stop in Hannibal was at Lover's Leap, which is a small park with panoramic views of the river and Hannibal. There's one picnic table.