The easiest way to reach the fortress is by the Yüce Yol Sok. highway, because it is dangerous to cross the slums (dogs, abandoned houses, construction site).
Entrance to the fortress is free, to the underground city too (it is located under the tower, a separate path leads there, a landmark is a wooden caretaker's booth). You can get around everything together in about 30 minutes. Good view of the city from the observation decks.
I think it's even more beautiful here in warm sunny weather.