Swimming pools in Seoul?

Hi there, My family and I will be traveling to South Korea in June and are looking to stay in a hotel in Seoul for at least part of our time. I know there's a decent hotel pool at the Hotel Shilla, where we stayed when we went 8 years ago, but I'm wondering if anyone has stayed at the Grand Hyatt, or somewhere else with a good lap pool. I have a 10-mile swim scheduled for a month after we get back so I have to be able to get in some decent yardage while we are there. Thanks!