This photo was taken from inside the Budapest Whale, which is sometimes called the CET Building. The Whale is a building that houses galleries and shops on the Pest side of the Danube. It’s so named because one end of it is a gracefully shaped glass and steel construct that is reminiscent of a whale shape. Hence the light traveling through onto the water. (The other end is a more traditional red brick structure.)
One can see Freedom Bridge (Szabadság híd) and Gellért Hill in the background toward the upper right-hand corner.