Visegrad Castle is a good half hour's hike uphill from the Danube. Its impressively large walls provide some incredible views of the surrounding river valley (you see immediately why they put the castle here), and also contain the first of no fewer than three torture museums we encounter on our trip.
Just up the ridge from the castle -- past the parking lot and hilltop hotel -- is a "summer toboggan," something I'd previously encountered only on vacation trips to the Alpine Slide in Vermont. This one is a bit lower-rent -- the track is metal instead of concrete, and the sledders ram each other worryingly often -- but otherwise, it's a perfect bit of nostalgia, a bolt from the blue.