Even if you won't pay the admission fee to go up the tower, the open spaces at the base already are very scenic.
Head across to the other side where there is another observation area facing the historic centre of the city.
N Seoul Tower has been renovated and rebranded. Nevertheless, the views are still the same - definitely worth a visit.
There is also a staircase leading back down to near Myeongdong, which is more strenuous if going the other way than the sloping street on the other side.