Arcata is small enough to walk everywhere in the city center. The Plaza, the university, Redwood Park, and most restaurants and bars are within a twenty-minute walk of each other. A bicycle is ideal for getting around — the town is flat at its core and relatively bikeable.
By bus: Humboldt Transit Authority (HTA) runs local routes including the frequent Arcata-Eureka bus line, which connects the two cities about every thirty minutes on weekdays. Useful for getting to Eureka without a car.
By car: You'll need a car for the coastal dunes (Manila/Lanphere area), the Arcata Marsh (though it's a walkable 2.5 miles from the Plaza), and day trips to Trinidad, the Avenue of the Giants, or the Lost Coast. Parking is generally easy and free in residential areas, and available on the metered streets around the Plaza.