When I watched Ep 11, I thought this place is very familiar, is it Heyri and I can confirm it today.
The place where Writer-nim danced haha is the space under a building called the Step in Heyri, you can see a picture of it here on this blog.
Hapjeong Station Exit 1. Take Bus No. 2200 and get off at Heyri No. 6 Gate Bus Stop, that should be closest to The Step.
If you are going to this place, you can go to Forest of Wisdom that is also in Paju on the same day.