1. Nike flagship store - customize your own sweater, ball cap, t-shirt, or tote bag, with Seoul specific patches and designs. 2. Street food - try some Korean street food snacks! 3. Olive Young - indulge in some K-beauty at Korea's preeminent skincare/makeup store. Think Sephora or Ulta, but K-beauty.
Explore one of the largest Korean palaces in the middle of the metropolis. If you rent a hanbok in one of the nearby rental studios, you can get free admission.
Take a cable car for an amazing aerial view of the city. You can leave a lock to commemorate your visit. Legend says if a couple leaves a lock together, they'll stay together ("locked") forever.
Enjoy some local street food at one of the largest markets in Seoul. You can find stalls selling a little of everything, not just food.