Verkiai is the green, northern edge of Vilnius, best known for its former palace estate and wooded parkland above the Neris River. It is not an essential first-day sight, but it shows a quieter side of the city beyond the Old Town and the usual museum circuit.
Come for a walk, the river views, and the remains of the aristocratic estate rather than for a single blockbuster building. It pairs well with a slower day in Vilnius, especially if you want trees, paths, and a little breathing room after the centre.