We took the subway to the Gallery baths and then walked up the hill to the citadel.
There are several ways up some zig zag and others have steps and it is about a 30 minute walk.
There is shade from trees most of the way up and the reward at the top is great views over the Danube river and the city.
We went in the late afternoon which provided great light.
There are large crowds at the top but the view is well worth the effort.