• Tagged Acadia, Acadia National Park, architecture, bridge, Cadillac Mountain, carriage, environment, forests, islands, kayaking, Maine, Mount Desert Island, mountains, National Park, nature, ocean, places, Thunder Hole, travel, wetland, wildlife, woods

Acadia National Park along the rugged coastline of Maine may not be the first place that jumps to mind when thinking about America’s busiest parks, but maybe it should come to mind in the top 10 because it was the 9th most visited U.S. national park in 2011 with over 2,300,000 visitors. Acadia and Cuyahoga switched places from 2010, when Cuyahoga Valley National Park was ranked 9th in visitors. Acadia National Park protects more than 47,000 acres of lakes, ponds, woodlands, granite-domed mountains, and ocean shoreline along the coast of Maine. There are more than 140 miles of hiking trails, 45 miles of historic carriage roads, and scenic park roads for drivers. Diverse wildlife, waterfalls, cliffs, stone bridges and scenic vistas can all be found on this cluster of islands that make up Acadia. Hikers, bikers, horseback riders, kayakers, climbers, bird watchers and photographers are among the nature lovers who visit Acadia National Park. [40 Photos]

• Tagged adrenaline junkies, adrenaline rush, canoe, extreme kayaking, extreme sports, Great Falls National Park, kayak, kayakers, kayaking, Oregon, rivers, waterfall, whitewater, whitewater kayaking, whitewater river rapids

There are many types of kayaking which can include paddling down gently moving water, but these kayakers are into demanding, dangerous whitewater. If trapping your legs into the cockpit and kayaking over insanely treacherous whitewater river rapids is not enough of an extreme adventure sport, then how about going over a waterfall in a kayak? Professional kayakers drop hundreds of feet going over falls. Extreme sports photographers captured these whitewater kayakers river running, rolling, creeking, playboating and during other extreme kayaking. We’re not quite sure if these kayakers are on drugs . . . or need to be. Or maybe all these adrenaline junkies need is the natural drug, an adrenaline rush? [45 Photos & 5 Videos]