Spend the day at the Chamonix Sports centre - saunas, steam and large swimming complex. There is an Olympic outdoor pool with area for sunbathing and two indoor pools, one with large fun slide which is great for kids of all ages.
Mont Blanc Plage: About 15km from the apartment is an area known as Mont Blanc Plage - a series of lakes each designated for swimming and sun bathing or fishing or water sports such as wind surfing. The lakes are clear and warm and the beach has a great family atmosphere. It's a lovely place for a picnic.
Spend a relaxing day at the Thermal Spa in the Park Thermal in St. Gervais which offers various water massages and beauty treatments. Further details