The Citadella was built during the time when the Habsburgs ruled Hungary in order to help defend the city of Budapest.
While the Habsburgs said the Citadella was to defend Budapest, it was built shortly after an attempted revolution by the Hungarians to overthrow the Habsburgs in 1848-1849. The Citadella is located at the top of Gellert Hill along with the Independence monument.
To reach the Citadella you can walk across either the Independence (Szabadsag) Bridge or the Elizabeth (Erszebet) Bridge (the big white bridge) and then up the pathways that lead to the top of the hill. The Citadella does charge for admission (300 or 400 Ft) and is open from 8am – 10pm daily. The views over Pest in the evening are fantastic!