Szent István Park (Saint Stephen Park) is the green heart of Újlipótváros, a formal rectangle of lawns and plane trees running down to the Danube embankment. The buildings around it are a showcase of 1930s Hungarian modernism — clean white Bauhaus apartment blocks that were the height of fashion when they went up and remain among the most coveted addresses in the city.
There is not much to "do" here beyond sit, stroll, and watch local life: families, dog-walkers, old men playing chess. The view across the river to the Buda hills is lovely, and the Dunapark café on the corner is a fine spot to take it in. The bridge to Margaret Island is a few minutes' walk north.