Many people ride the Namsan cable car up the mountain, which gives a great view over Seoul, and is really beautiful at night. Then people get off the cable car and walk to the tower.
The tower has restaurants and gift shops on the ground floor as well.
There's 4 observation decks, and on the 4th one is a restaurant, which actually rotates tih a rate of one revolution every 48 minutes.
You can see the whole city from top, and it has a really great view, and it's therefore really common for couples to go there.
In november 2011, the place had about 2,000 foreign visitors, and they decided to hang padlocks on the Tower fence as a symbol of love as their favorite activity in Seoul.
Namsan cable car.
The locks on the Namsan fence.
The view at night.