Stay: In October I stayed at Hyundai Residence, a serviced apartment located in Chungmuro 5-ga. The apartment has 2 metros close by (5-10 minutes walk), Dongdaemun History and Culture Park and Euljiro 3-ga. It was a bit difficult to find as it was nestled in one of the alleyways but this card from a kind concierge, from another hotel saved me. The apartment was very spacious, clean and had a nice view where you can also see Namsan Tower in the background. The room also included a kitchenette and washing machine. On the ground floor there is a 7-Eleven mart and a cute teddy-bear cafe.
In June I stayed at Staz Myeondong 1, which is literally 1 minute walk away from Euljiro 3-ga station and about 10 minutes walk to the centre of Myeongdong. The location is very convenient and it also has a 7-Eleven on the ground floor. However the walls are very thin and I was able to hear the neighbouring rooms clearly; the wifi in the room was very weak, the duvet and covers were rough and the aircon sounded like it had reached its dying days. They did have a cute green initiative though, every time you did not want to have your sheets changed just leave the card on your bed and they leave a brownie for you.
Do: Namsan Tower; I took the Namsan Oreumi (outdoor elevator) from Namsan Tunnel 3 to get to the cable cars which is free however you can also walk to the cable cars which will take roughly 15-20 minutes. An adult return ticket for the cable cars is 8,500 won. An adult ticket for Namsan Tower's observatory is 10,000 won. The tower itself and the area around it is beautiful, it is easy to see why it is popular as a dating spot, however the view from the observatory was hindered by the dirty windows.

COEX Mall and Aquarium, when I went in 2013 COEX mall was undergoing renovation but thankfully the aquarium was still open. This was surprisingly really good and pretty big for an aquarium located inside a shopping mall. An adult ticket is 25,000 won.
Cheonggyecheon Stream runs for 8.4km across some of Seoul's tourist attractions including Deoksugung Palace and Insa-dong Street which makes it easy to visit after exploring other places. Depending on which part of the stream you go down to, at night the lights look beautiful.
Myeongdong is a shopping haven, I always make sure to stock up on my skincare here and I love the fact that they always give you so many freebies with your purchase. It is a tourist spot so you will have shopkeepers standing outside shouting in Chinese (Mandarin) and Japanese, trying to entice customers into their shops but there is also a lot of restaurants and the night food-market to visit here. Ewha Women's University is also good for shopping, it has a lot of stalls and boutique shops filled with cute accessories and clothes. Afterwards you can pay a visit to the University ground which is partly open to visitors.

Lotte World Amusement Park is an indoor amusement park set with an ice-skating rink, shopping mall, theatre and museum. Ticket prices decrease after 4pm and 7pm so I only paid 18,000 won for an adult adminissions-only ticket after 7pm and paid for rides separately. This worked out for the best as most rides had queues over an hour. I ended up going on only one ride which was the hot air balloon ride which circles above the themepark, giving you a birdeyes view of the entire place.
The five palaces of Seoul; Gyeongbokgung Palace, Deoksugung Palace (and the guard-changing ceremony) and Changdeokgung Palace (and the Secret Garden). The 3 palaces I went to are beautiful and admissions are cheap. You can get an integrated ticket for 10,000 won which gives you access to all the palaces and is valid for 3 months for use. The guard change at Deoksugung is interesting and takes place 3 times a day at 11am, 2pm and 3:30pm.
Bongeunsa Temple, I was lucky enough to visit the temple for Buddha's birthday so the temple was lit up by lanterns everywhere, with a lot of people writing their prayers and wishes and attaching it to lanterns.
Bukchon Hanok Village is a traditional Korean village located between Gyeongbokgung Palace and Changdeokgung Palace. Amongst the traditional houses there are also cafes and workshops open to visitors.