I studied in North Korea for a month. The isolation shocked me the most.

• Todor Merdjanov recounts his month studying at Kim Il Sung University in North Korea.
• He attended intensive language classes by university professors while also exploring Pyongyang and further afield.
• Merdjanov later studied in South Korea, noting similarities and reflecting on his time in the North.

This as-told-to essay is based on a conversation with Todor Merdjanov, 33, a Bulgarian university student who spent a month in September 2013 attending Korean language classes at Kim Il Sung University in Pyongyang, North Korea.

Merdjanov currently works as a copywriter for a digital-marketing agency and an official translator for the Bulgarian embassy in Seoul, South Korea. The following has been edited for length and clarity.

It's been over a decade since I sat in the water of a Pyongyang public bathhouse, fielding questions from several North Korean university students.

The communal bathhouse is a place for bonding and chatting with friends. It's a cultural staple in both North and South Korea.

It was also a very strange experience to be paddling naked next to the other students from my dorm at Kim Il Sung University in the capital city of North Korea .

I had been studying at the country's oldest university for several weeks, and with almost no opportunities to contact the outside world, I had come to see these students as my friends.

Life at Kim Il Sung University differed greatly from my time as a 22-year-old student of Korean Studies in Sofia, Bulgaria.

When I accepted the offer by my professors to travel to the mysterious nation — with no safety instruction besides what we had learned about the Koreas in our lectures — I was excited to meet North Koreans firsthand.

A classmate and I arrived in Pyongyang after a short flight from Beijing on a hot September day.

We were shown around our accommodation, which we shared with around 35 North Korean, Chinese, Vietnamese, and Mongolian students.

We were given the rules for our trip by the housing manager, a North Korean man in his 40s employed by the university who oversaw the residence: We could only travel a short distance from the dormitory alone, always ask permission to go further, and respect the curfew of 9 p.m. for all international students.

All the university students wore uniforms. Men wore a white shirt and a dark red tie; women wore a white shirt and a dark, pleated skirt.

Everyone, both within the university and outside, also wore a metal badge with the faces of Kim Il Sung, the founder of North Korea, and Kim Jong Il, the recently deceased leader.

Students had lectures Monday through Saturday, with Sunday as the only rest day.

Students took turns cleaning the hallways and gardens of their university in between classes, a custom in schools across East Asia.

My Bulgarian classmate and I were given our lessons separately from the rest of the North Korean student body. We had two seminars a day, one on Korean reading comprehension, another on Korean conversation, and an extra class on Saturday.

Classes at Kim Il Sung University were hard work. My exchange partner and I would spend hours completing homework and memorizing hundreds of new words a week. We would often be asked to summarize complicated texts based on North Korean folktales or the life and achievements of Kim Il Sung, the country's founding leader.

Ideology was integrated into the curriculum. Our role was always to learn the language and better understand North Korean culture.

We were given more access to Pyongyang than your average tourist

I spent a lot of time exploring.

Although we were only supposed to go as far as the few shops for foreigners located in the streets outside the dorm, we asked the other North Korean students how far they thought we could wander.

We explored the town center and local shops and rode the subway a few times.

We were only asked for our passports once from a soldier in the street. Our palms sweating, he made a phone call and then handed back our documents. We scurried back to the dorm as fast as we could. No one mentioned the incident.

Our North Korean friends accompanied us on every official excursion . We often played games together, shared snacks, and talked about our lives at home.

One day, a group of North Korean students told all the foreigners in the dorm to dress formally and to meet in the lobby. We couldn't take our keys or wallets, and none of us knew what was in store.

After being loaded onto a bus, I realized we were headed to the Arirang Mass Games .

The show is the world's largest gymnastics display and one of the most important events in the North Korean calendar. It has included over 100,000 performers at past events.

We were seated in a section of the stadium reserved for foreign students and diplomats.

What looked like tens of thousands of North Korean children and adults played music, gave traditional dance performances, and conducted intricate gymnastics routines. Colored lights and lasers danced around the crowd, and fireworks cracked overhead.

The spectacle of the Mass Games is the scale of the participation. We knew we had just witnessed something that few people outside North Korea would ever see.

Saying goodbye, knowing we'd never be back

After four weeks in the country, it was time to say goodbye.

As soon as we arrived in Beijing, I video-called my parents. In Pyongyang, I had only been able to call them twice: once from an international hotel and once during a visit to the Bulgarian embassy. Each call was only a couple of minutes long.

During my exchange, I spoke to young North Korean people, asking them about their ambitions. Many students wanted the same things as we did: to travel and experience the world. I was discouraged and sad, knowing they could not travel as I had.

Two years later, in 2015, I went on another university exchange, this time to South Korea.

We were allowed to visit the 38th parallel, the demilitarized border zone between North and South Korea.

On the way there, the other exchange students chatted excitedly over the opportunity to glimpse such a forbidden country.

As I gazed over the border to the North Korean hills and fields in the distance, I could vividly see the names and faces of people I knew there. Knowing that I would never see or speak to them again, I wondered, sadly, what they were doing now.