Explore the volcanic coral gardens of American Samoa, the sea lions and elephant seals of the Channel Islands, and the warm, clear waters of the Virgin Islands National Park.
Majestic geysers plunging out of the earth are Yellowstone National Park's claim to fame. Where can you experience geothermal features from an underwater vantage point.
Tall Trees Grove is a bucket-list hike for many, but if you choose to look down rather than up, Redwood Forest National Park has other treats in store.