The Oregon Country Fair is one of the Willamette Valley's great annual rituals, a three-day mix of handmade art, performance, food stalls, music, costumes, and deeply Eugene-flavoured counterculture. It takes place outside town near Veneta, but it belongs culturally to Eugene as much as any downtown landmark.
This is a date-specific POI rather than an everyday sight, so it only matters if your trip lines up with the July fair. If it does, plan transport and tickets early; the event is popular, deliberately low-key in infrastructure, and much better approached as a full-day immersion than a quick stop.