Kongguksu is what Korea eats in the worst of the summer heat: thin wheat noodles sitting in a chilled, unsweetened soy bean broth, served so cold there are ice cubes floating in it. It is nutty, savoury and almost completely plain.
Everything rests on the broth, so blend it longer than feels necessary and chill it properly. Season at the table too; many households put the salt on the table rather than in the bowl.