BEST AT NIGHT
The water temperature at Sand Beach, Acadia National Park's popular swimming area, rarely exceeds 55 degrees, so don't even think about skinny-dipping in those Maine waters. Far better to stroll at night -- and bundled up -- when the shimmering bioluminescence from microscopic creatures in the bay can sometimes illuminate the adjacent rocky bluffs. Pick up Ocean Path behind the beach restrooms for the 4-mile walk to Otter Point and back. Take it slowly in the dark. Lot parking is available, plenty of it after hours.