A lightweight linen cover up dress is what you wear over a swimsuit when you are moving from water to lunch to shopping without actually getting dressed. Linen is the only fabric that actually stays cool and looks better the more you wear it. The construction should be loose enough to move freely but shaped enough to look like you made an effort. A knee length keeps things practical and proportionate. Choose a solid in white, natural linen, or a warm neutral that complements rather than competes with your swimsuit. These slip on over damp skin without clinging and dry quickly enough that you can change your mind about where you are heading. The simplicity is the whole appeal.