There are a lot of options to go to Nami Island, Petite France and Garden of the Morning Calm. From Seoul, you can rent a car or avail of the tourist bus which are two of the most convenient ways to get there but can also be costly. You can also commute via ITX or metro subway. I usually use the metro subway which only cost ₩4,500 round trip from Myeongdong (where I usually stay) to Gapyeong Station. From Gapyeong Station, you can either hire a taxi to take you there or avail of the Gapyeong City Tour bus for ₩6,000).
It will be helpful if you will also download the subway application on your mobile phone so you have a detailed guide of the fare, timetable, and options of which route to take (fast or simple). I took the faster route which has 1 hour and 46 minutes travel time. The simple route has the least transfers and will take 2 hours and 4 minutes.
Here is the step-by-step guide on how to commute from Myeongdong to Gapyeong to get to Nami Island and Petite France. If you have the subway app, you can just change the place of origin and follow the guide.
1) From Myeongdong station, I took line 4 train heading to Chungmuro station to get to Dongdaemun History and Culture Park station.
2) From Dongdaemun History and Culture Park station, I changed to line 2 and took the train heading to Sindang station to get to Wangsimni station.
3) From Wangsimni station, I changed to Jungang line and took the train heading to Cheongnyangni to get to Mangu station.
4) From Mangu station, I changed to Kyeongchun line and took the train heading to Galmae station to get to Gapyeong station.
5) From Gapyeong station, I took the Gapyeong City Tour Bus which is a very efficient and practical option if you want to visit the major tourist attractions around the city for only ₩6000. Gapyeong Tourist Bus Route includes Ehwawon Camping Site, Gapyeong Rail Bike, Nami Island, Petite France and Garden of the Morning Calm. The loading and offloading area of the tour bus is just in front of the Tourist Information Office which you will easily see upon exiting Gapyeong Station.
If you arrived really early in the morning and the bus is not yet available, you can just take a taxi to go to Nami Island. If you are travelling as a group, this can cut down the transportation cost and even save you time since the earliest shuttle service starts at 9 a.m.
Here is the Gapyeong shuttle bus route and time table during my travel. For updated information, you may visit http://www.gptour.go.kr.
The bus stop for Nami Island is before the parking lot. You will have to cross the street and walk your way through the parking lot until you reach the entrance to the ferry dock of Nami Island. Look for the Nami Zip Wire and it will lead you there.
If you arrived late afternoon like I did but still wanted to tour around, I suggest you go to Petite France first then Nami Island. That way, even if you will not be able to make it until the last shuttle bus schedule, at least you can take a taxi from Nami Island which would cost only around ₩3,000-₩3,500 because it is very near the subway station, while taxi from Nami Island to Petite France is about ₩17,000 to ₩18,000.
Here is a more detailed guide on how to go to Nami Island from their website: https://namisum.com.
The bus stop for Petite France is on the same side as its entrance. You will just have to cross the street to get to the bus stop going back to Nami Island and Gapyeong Station.
Here is a more detailed guide on how to go to Petite France from their website: http://www.pfcamp.com
Garden of the Morning Calm
The last stop of the shuttle bus is the Garden of the Morning Calm. I was not able to go to Garden of the Morning Calm because I do not have enough time since I arrived late in the afternoon and the travel time by shuttle bus from Gapyeong Station is 45 minutes one way. However, the above steps using the subway as well as shuttle bus or taxi would still be the same if you will go there.
Here is a more detailed guide on how to go to the Garden of the Morning Calm from their website: http://morningcalm.co.kr.
I hope the detailed instructions have been helpful, please feel free to comment and share your experience too! I traveled solo during my first trip to Korea and went to Nami Island and Petite France on my own, I just researched and asked questions. When in doubt, take time to review your map or ask the The Tourist Information Office for assistance.