@kpopandkimchi About one of the creepiest dramas I have seen (also the very first drama I watched) is Gap Dong.
20 years ago Moo-Yeom’s (Yoon Sang-Hyun) father was a suspect in the "Gap Dong” serial murder case. Because of the detectives’ oppressive investigation, Moo-Yeom’s father killed himself. Now, Moo-Yeom is a detective and works to capture the killer Gap Dong. The statue of limitations has expired for the serial murder case and Moo-Yeom resigns to the belief that Gap Dong is dead. New clues though for Gap Dong appears in front of Moo-Yeom and he sets out to catch him once and for all.
Here is the trailer sorry if it is not subbed.
*somewhat of a spoiler* The creepiest part for me is the whistle.
If you do watch you should let me know how you like it. This drama means alot to me because it introduced me into the wonderful Kdrama and KPop world :)