Hainburg Castle

The Heimenburg (or "Hainburg") is the ruin of a hilltop castle above the town of Hainburg on the Danube in Lower Austria.
According to legend, it takes its name from Heimo, the cupbearer of Arnulf of Carinthia, who commissioned it with the construction of a church and a castle (today's Bad Deutsch-Altenburg).
1042 were this castle in Bad Deutsch-Altenburg by Henry III. destroyed. At that time the chronicler Hermann von Reichenau called the "Heimenburg (Hainburg) and Brezesburg (Bratislava) very populous cities".
Emperor Henry III. ordered around 1050 at the Nuremberg Congress to build on the castle hill in today's Hainburg on the Danube, the Heimenburg new. It was destroyed in the 2nd Turkish siege in 1683. After 1742, due to the construction of the new castle at the foot of the castle hill, the decline of the castle occurred. (Wikipedia)

Hainburg is always worth a visit - water, gastronomy, cool mountains

Great view, but you can't cycle all the way up.