The Cascades divide Washington into a wet western half and a dry eastern one, and crossing them is the single most useful weekend decision available from Seattle.
The islands
The San Juans — drive 90 minutes to Anacortes, then a Washington State Ferry to San Juan, Orcas, Lopez or Shaw.
Vehicle reservations are strongly advised in summer and fill early. Passenger-only sailings and seaplanes also run direct from Seattle.
Orcas has the highest point and Moran State Park; San Juan has Friday Harbor and whale watching; Lopez is flat and the best for cycling.
Bainbridge and Vashon, direct ferries from downtown Seattle, for an easy overnight.
Whidbey Island, by ferry or the Deception Pass bridge.
The volcanoes and the rainforest
Mount Rainier, two and a half hours — Paradise and Sunrise for alpine meadows, with wildflowers peaking in late July and August. Timed-entry reservations have been introduced for peak periods; check current requirements.
Olympic National Park, two and a half hours plus — three distinct sections hours apart from each other: Hurricane Ridge for mountains, the Hoh Rainforest for temperate rainforest, and Rialto and Ruby beaches for the wild coast.
Pick one section per weekend. Trying to do all three is a driving trip.
Mount St Helens, three hours — the blast zone, still visibly recovering.
The dry side
The answer when Seattle is grey, which is often.
Leavenworth, two hours over Stevens Pass — a Bavarian-themed town that leans hard into it, with genuine mountain scenery around and the Enchantments hiking area beyond, which requires a permit lottery.
The Methow Valley, four hours — Winthrop, hiking, and one of the largest cross-country ski trail networks in the country.
Lake Chelan, three and a half hours — a long glacial lake with wineries and reliable sun.
Walla Walla, four and a half hours — the state's best wine region, and a long weekend.
North and south
Vancouver, BC, three hours — a genuinely different city. Border waits vary substantially; check before setting out and carry a passport.
Portland, three hours — bookshops, food carts, and the Columbia River Gorge on the way with Multnomah Falls.
Practical
Mountain passes close. The North Cascades Highway typically shuts from around November to May for avalanche danger, and other routes close in storms. Check the state transportation department before any winter or shoulder-season crossing.
Park passes — an annual national parks pass pays for itself quickly here.
Ferry reservations for the San Juans open on a staged schedule and fill; book as soon as they are available.
Summer is the dry season. July through September is when the mountains are open and the rain stops.