You can stay on this one-acre, two-campsite spit, at the elbow of the Salish Sea, only if you arrive by man- or wind-powered means, so your neighbors are kayakers, not powerboaters (campsites, $9; parks.wa.gov). Catch the ferry from Anacortes to Friday Harbor (from $35; wsdot.wa.gov/ferries). Drive ten miles to Roche Harbor and rent a sea kayak (sanjuanislandoutfitters.com) for the easy quarter-mile trip to Posey, and watch out for breaching orcas as you dip your paddle.