WHERE: More than 450 isles form the San Juan Islands — an archipelago that sits pretty between mainland Canada, Vancouver Island and Washington state's northwestern coast — yet only four receive daily ferry deliveries of visitors. And, my, how they come. Throughout the year, more than a million folks disembark onto Orcas, Lopez, Shaw and San Juan islands. The invasion peaks this month, when temperatures hover at a pleasant 70 degrees and the orcas are still at play. (Fret not, off-season travelers: The region boasts an annual average of 247 days of sunshine and half the rain of Seattle.)

HOW TO TRAVEL: The finest way to travel around the Puget Sound landfalls is via Washington State Ferries, the largest ferry fleet in the United States. The vessels serving the San Juan chain depart from Anacortes, on Fidalgo Island, the easternmost of the San Juans. The boats travel west — Lopez to Shaw to Orcas to Friday Harbor on S.J. Island — and the ride can last up to two hours, depending on stops. Passengers pay only to go west; eastbound trips, including the one back to the mainland, are "free."

Year-round boat service starts around dawn and ends long after the witching hour, with multiple departures in between. The ferries take bikes and cars (plus trucks, mobile homes, etc.), but before you queue up, double-check the timetable: With so many incoming and outgoing boats, the schedule can be difficult to crack. (Ferry officials are used to this confusion, so ask away.)

The frequency and ease of on-water travel encourage island-hopping. You can spend your entire time on San Juan Island and plan side trips to the other islands, or split your nights among two or three or even all four.

Indeed, each isle has its own personality and mystique: San Juan boasts a vital, sophisticated downtown, British-American intrigue (involving a pig) and whale-watching by shore and sea; Orcas, the largest isle and the one with the highest peak, features arts and parks; Lopez, a patchwork of farmland and beaches, is called the "Friendly Island" because of its wave-happy residents; and Shaw is a low-key affair steeped in nature.

Of course, the fun is not just land-based; getting there is equally entertaining. The boats are as large as cruise ships and come with cafeterias, capacious work/ read/zone-out spaces, outdoor seating and stunning views of water and wildlife, including, if you're lucky, the summering killer whales.

INFORMATION: For schedules, prices and reservations, Washington State Ferries 206-464-6400, www.wsdot.wa.gov/ferries.