Gyeongbokgung Palace was originally constructed in the 1300's and has been under ongoing reconstruction and rebuilding since the Japanese occupation in 1911. The two palaces we visited were sprawling and beautifully landscaped. They were inexpensive to enter and the other palace we visited didn't even charge us for Elliot.
The Children's Grand Park
There were playgrounds, and performances, but we spent most of our time looking at the animals. It had animals found in any world class zoo, I was surprised there wasn't any fee for the attractions or park.
This river had been covered by concrete in 1968 for roads. A 900 million dollar project had it restored to a flowing stream in the heart of Seoul in 2005. It really is a nice oasis in the middle of the city, the kids enjoyed playing up and down it.
Seoul Metro system appeared to me safe and clean. We didn't find it as efficient and simple as Hong Kong, but I am beginning to think not many subway systems are as excellent as the HK MTR, and the Tube. The most confusing part was duplicate names of transfers or stations assigned a different number. Nathan being the good navigator always figured it out. It was sufficient and got us around. We did not take a single taxi or bus (aside from airport bus) during our time.