Easy! If you are in Seoul, some to Chuncheon city by subway and get off the train in Namchuncheon satation. Just jump in bus number 12 and get out at the last station! You need to pay 1100 won for the bus. If you are around Myong-Dong underground market in chuncehon then take line 11 and after 20-30 min you will be at the last station.
The place is caled Soyang Dam. Beautiful place, with the view of a nice valley, the dam and green forests. If you can try to be there before 10 so that you can probably see the mysterious morning fog all over the lake.
From Soyang dam buy a round ticket to the starting point just for 6000 won and enjoy your ride on the ferries. Quite cheap, quite nice.
Time to walk
A 5 minute walk will take you to few restaurants, a good place to eat something if you like and also to sit for a while.
Before starting you can take a look at the routs map, in Korean and not accurate, but still worth a look.
Depending on you speed you will get to the temple in 30-45 min.
On the way
Not only the forest and small waterfalls on the route are beautiful but there are also some extra attractions!
Good to know
If you can try to go to Cheonmyeong-sa on Sunday. This way there might be some extra program available in the temple and also there is a chance that you can try temple food!
I for got to check the temple elevation! it should be something about 400 meters.
After the temple you can experience real hiking! nice trails with some adventure...
As you go higher, in some places you will have a great view of the lake, mountains and the temple.
You can do the whole program in a half day and really enjoy. few hours of activity with different types of fun.
Suggestion...If you like there are lots of routes to hike more if you want. That's up to you. But as I saw the area, I wouldn't suggest that.
Hiking trail after the temple to the top