Your tour guide will bring you here because it's the site a famous (in Asia) Korean Romantic Drama.
So, guess how fun the island is for people not in romantic mood?
Do bring a spouse, or maybe your wife and kids. But bring a spouse.
Then take a lot of silly pictures which pose is dictated from scenes from the movie.
Then watch some Asian ladies taking silly poses with bronze statues of the actors and actresses from the movie.
It's a beautiful stroll nonetheless. Calm. Scenic. If gives a good counterpoint to the urban nature of Seoul.
The ferry ride is nice, the walk is nice, the facilities are decent.
I don't know if there's fee, I was part of a tour group, it could be inclusive in our tour cost