There is a high turnover rate for English teachers in Korea and new jobs open up all the time. The main centers of work are big cities like Seoul, Busan, and Daegu but you should be able to find a job just about anywhere in the country if you look around. Also, there are a number of recruiters in Korea and they often have leads about jobs all over.
However, you should keep in mind that, at 1 million won+ per pop, recruiting English teachers is big business in Korea and some people are more interested in making a quick profit than helping foreigners find the best possible workplace. You should ask for references from any recruiter and be sure to contact several former teachers to find out about their experiences with them.
Check out the following websites to help you find a job teaching English in Korea.
Many ESL teachers in Korea are also switching over to other careers when they go back to their home countries. The free time you have can be used taking online courses. Just a couple examples: some people study online masters degree programs in education while they are teaching and some people even study through online schools for estheticians. I am not saying that everyone should spend all their free time in Korea studying but you can definitely make the most of your time with these online programs.