SIHEUNG, Gyeonggi Province — Local travelers who judge a destination by the number of attractions tend to look east, toward the deep blue water and fine sand beaches that fill summer travel supplements. The West Sea close to Seoul and its metropolitan area has long been treated as the consolation prize — flat, brown at low tide and governed by a tidal range that rearranges the shoreline twice a day. Yet, those who would like the coast for tranquility and reflection will find this stretch offering exactly that at a price nobody has thought to advertise. Siheung, a city of more than 500,000 in Gyeonggi Province, sits about 40 kilometers southwest of central Seoul and holds two coastal destinations — Geobukseom and Oido — of entirely opposite temperaments. Geobukseom, which literally translates as “Turtle Island,” is an island of marinas, surf lagoons and glass towers that has not yet filled up. Oido, some 10 minutes away, is a former island that has been grilling shellfish for day-trippers for decades. The "turtle" is not without its reason. Pull Geobukseom up on a map and the o