Large and well secured complex

Surrounded by double fencing, well build, and obviously very advanced. Probably some kind of research & development plant, with extensive underground infrastructure. Possible underground railway connection with an underground naval base to the north-east. Possible existence of underground railway station (see ventilator / air circulation station).

Thanks for user handydandy61 for the following info:
- chemical research facility and development plant. There is also a university research campus (Hamhung University of Chemistry) within the complex. The specialized train lines are those DPRK military-only railways. The train line is presumably used to transport weapon technology, as well as ferrying leadership and scientists.