The Citadel on the top of Gellért hill is being renovated, and unfortunately the entire area is closed because of the construction works. It also means that a truly popular tourist attraction of Budapest is closed and it’s impossible to enjoy the most magnificent views over Buda and Pest. The very bad news is that it remains closed for another few years and it’s impossible to estimate when it reopens. It’s just my personal opinion that they could have left a little path open for the tourists to enjoy the view, but that’s not the case.
You can still take a walk on Gellért hill, and you can climb to the statue of Saint Gellért from where you’ll have a great view over the Pest side of the river.