This is an out-and-back beach running route that connects three islands by crossing the water between them. The route begins and ends at the pier on Isle of Palms and travels the front beaches of Isle of Palms, Dewees Island, and Capers Island, turning around at the far northeastern tip of Capers Island and returning to the start. The route requires swimming Dewees Inlet and Capers Inlet twice each, totaling close to a mile of swimming in addition to 23 miles on foot.

Roots natuurpad is the longest "nature" hiking trail currently in the Netherlands. 

70% of the trail is on unpaved tracks. 

note: you need to pay entrance fee to cross the national park: de hoge veluwe.

More information here:  https://www.rootsmagazine.nl/langste-natuurpad-nederland/