Children's Grand Park reopens after 'bomb threat'... No explosives found (Seoul, Korea)

Children's Grand Park in Gwangjin-gu, Seoul, South Korea, which had been closed due to a threatening phone call claiming that "explosives had been placed at Children's Grand Park," has reopened its doors after multiple searches.
At around 8:20 pm on the 30th of last month, Gwangjin Police Station in Seoul received a threatening phone call saying, "An explosive has been placed at Children's Grand Park."
Police quickly evacuated the residents and began a search, but were unable to find any explosives.
Police conducted several searches into the early hours of the morning, but found nothing major. With no major abnormalities found, Children's Grand Park reopened to the public from 9 am that day.
Police are tracking the caller through telephone inquiries, but the investigation is reportedly proving difficult as there is no confirmed number.