Seaside's main attractions are outdoor and old-fashioned. The Promenade is the social spine of the town — a mile and a half of concrete boardwalk along the beach where you can walk, cycle, or sit and watch the waves. At the south end of the Prom, the Lewis and Clark Turnaround monument marks the historical endpoint of the Corps of Discovery's journey to the Pacific. The Seaside Aquarium, one of the oldest on the West Coast, sits right on the Prom with a harbor seal pool.
For something more strenuous, the Tillamook Head Trail is the best hike in the area — six miles of old-growth Sitka spruce, ocean views, and a hidden WWII radar station, ending at Cannon Beach. The beach itself is broad, flat, and good for kite flying, clam digging, and bonfires. Broadway, running from the highway to the beach, is where the bumper cars and salt-water taffy shops live — worth a walk for the atmosphere even if you don't stop.