Information about anything inside North Korea is hard to come by and not many know that the capital Pyongyang has its own metro system.
The capital’s underground is particularly secretive and access to foreigners has historically been restricted to only two stations, which gave rise to a conspiracy theory that the metro was purely for show. It was claimed that it only consisted of two stops and that the passengers were actors.
It was also rumored that due to the lack of electricity the carriages only move when visitors are scheduled to be in the system and that the same North Koreans can be seen getting on and off the carriages again and again.
However, recently some foreign tourists have been able to have a look at all stations across both lines of the Pyongyang Metro. They've posted detailed accounts of their trips with rare photos of the stations.
It is believed that the construction of the underground city transit system was started after 24-year-old Kim Jong-il, the son of then North Korean leader Kim Il-sung, visited Beijing in 1966 and was inspired by the construction of the new metro there.
Kim Il-sung wanted to demonstrate the superiority of North Korea over the South and prompted the network's construction in 1968, three years before the start of the Seoul Subway network (1971).
North Korea claims it has constructed the network solely on its own, however there is proof that it obtained a lot of its workforce from outside: the project was developed with the help of Soviet project designers, Chinese and Czech engineers and German rolling stock experts.
It's now claimed that Pyongyang Metro is the deepest subway system in the world; the tracks are located 110 meters underground. However the metro in Russia’s St. Petersburg also claims to be the deepest, based on the average depth of all its stations.
The Pyongyang network has a dual purpose: it doubles as an underground fallout shelter, with blast doors in place at hallways.
There is, however, much speculation about the existence of additional secret lines crisscrossing the city that are used only by high officials.
An accompanying rumor is that the military has a secret line crossing under the river.
It's believed that the Chinese postponed finishing the Beijing Metro in order to send their subway construction crews to North Korea to lend a hand.
With regards to its rolling stock, North Korea always claimed it had manufactured it domestically. However the media sources say that the first 4 rolling stocks (DK4 units) were built by China and were later on sold to the Beijing Subway, where they served in three car formations on line 13.
Since 1998, the Pyongyang metro has used former German rolling stock from the Berlin U-Bahn.
There are two different types of rolling stock: GI ("Gisela") former East Berlin stock, built between 1978 and 1982, and D ("Dora"), former West Berlin stock, built between 1957 and 1965.
All advertising though was removed and replaced by portraits of the deceased leaders, Kim Il-sung and Kim Jong-il.
A BBC journalist in 2000 reported seeing "old East German trains complete with their original German graffiti.
In 2015, Kim Jong-un rode a newly manufactured train which is reported to have been developed and built in North Korea, although the cars appear to be significantly renovated Class D cars.