Downtown Seattle, Pike Place Market, and the waterfront are walkable, and Link light rail reaches Sea-Tac Airport and several other neighborhoods, so a car is not essential for a downtown-focused trip.
Seattle Traffic Has a Real Reputation
Between I-5 congestion and the floating bridges across Lake Washington (I-90 and SR 520), driving here can be genuinely slow at rush hour. If your trip stays downtown and on the light rail line, skipping a rental avoids this entirely.
When a Car Helps
Day trips to Mount Rainier National Park (about 2 hours south), the Olympic Peninsula, or wine country in the Yakima Valley are all far more practical with your own car. A ferry to Bainbridge Island can be done on foot as a passenger, but exploring beyond the ferry terminal benefits from a vehicle.
Compare rental rates above if Mount Rainier or the Olympic Peninsula are part of your plans, or check flight and hotel options if you’re keeping things downtown.