If the weather isn't rainy, typhoon then it would be most suitable for sightseeing. In case of typhoon, there is no permission to swim in the sea.
The food cost is high for budget travellers. There are so much mountains, beaches for sightseeing, taking pictures and videos.
The city is really beautiful, have lots of beautiful island like Oedo Island and Jangsado Island. Try to go to Windy Hills if you can, it is really beautiful and windy.
The public transportation is bit problematic. We use taxi from Jangseungpo to Geoju Port (for Jangsado Island Ferry) and cost us about 31800won, but it hard to get taxi from Geoju Port. The man from the ferry terminal is helpful enough to send us to Windy Hills. From Windy Hills, you can take bus to Pabble Beach, then use another bus to go back to Jangseungpo.
Geoje-si is easily accessible from any part of the island. The city is riddled with western restaurants and foreign markets.
It resembles Itaewon in Seoul because of the vast numbers of foreigners living there.