I just made some pictures here the other day as I walked across the Petöfi Bridge in Budapest with my beautiful wife (much more gorgeous than the view from the bridge). Below you can see some of the results. At the pictures you can see the Gellert Hotel, the Gellert Hill, the Elisabeth Bridge and the Castle in the background.
The best way to see all of these by night is doing a boat trip on the Danube, which you can find more information about here.