If your idea of a good vacation means being near the water, head to Seoul Floating Islands. Whatever you choose to do here, you're unlikely to get bored of those pretty views.
Seoul Floating Islands is often on the itineraries of travelers to Seocho-gu. But this water-surrounded land mass shouldn't be your only stopover around this part of town. Gyeongbokgung Palace is not too far away and worth a look.