Spend the morning exploring downtown. Visit the Portland Art Museum or the Oregon History Center, stop by the historic First Congregational Church and Pioneer Courthouse Square, and take a stroll along the Park Blocks or Waterfront Park. Eat lunch and do a little shopping along Northwest 23rd Avenue in the early afternoon, and be sure to get a look at the beautiful historic homes in Nob Hill. From there, drive up into the northwest hills to Pittock Mansion, and finish off the afternoon at the Japanese Garden and the International Rose Test Garden in Washington Park. If you still have energy, head across the river for dinner on Hawthorne Boulevard; then drive up to Mt. Tabor Park for Portland's best view of the sunset.
On your first day, follow the itinerary above, but stay on the west side for dinner, and take your evening stroll in Waterfront Park. On your second morning, visit the Lan Su Chinese Garden in Old Town, and then head across the river to the Sellwood District for lunch and antiquing. Stop by the Crystal Springs Rhododendron Garden; then head to the Hawthorne District in the afternoon. Wander through the Hawthorne and Belmont neighborhoods for a couple hours, stop by Laurelhurst Park, and take a picnic dinner up to Mt. Tabor Park to watch the sun go down. In the evening, catch a movie at the Bagdad Theatre and Pub, or get a beer at one of the many east side brewpubs. On Day 3, take a morning hike in Hoyt Arboretum or Forest Park; then spend your afternoon exploring shops and galleries in the Pearl District and on northeast Alberta Street. Drive out to the Grotto, and then eat dinner at the Kennedy School or one of the other McMenamins brewpubs.