It's no accident that North Korea's most sacred buildings are its largest.

According to Nick Bonner, a tour guide for Koryo Tours who visits once a year, the leaders of the country aim to prove North Korea's might through its architecture, most of which is made of bulky concrete.

That includes the May Day Stadium, a colossal structure built in 1989 and remodeled in 2014 that seats 150,000 people. It is the largest stadium by capacity in the world.

While it hosts some soccer matches and general athletic competitions, May Day's grandest and most elaborate events are the annual Mass Games (known in Korean as Arirang). They pay tribute to the country's history, founders, and current leaders through gymnastics and dance performances put on by thousands of participants.

The spectacle is often as grandiose as the venue itself.