Hike up to the Three Crosses Monument
For the best sunset spot and a viewpoint to see the stunning nightscape of Vilnius, it has to be at the Three Crosses Monument, a hill behind Vilnius Cathedral that you can climb. The Three Crosses Monument was built on top of the old wooden cross-site that was erected way back in the 17th Century and became an integral part of the city until it was taken down by the Soviets. The city reconstructed it after gaining independence to remind itself of the dark past during the Soviet reign.
As it turns out, it is also a great viewpoint to see the unobstructed skyline of Vilnius and it is one of the popular places for locals to hang out at sunset. The hill is pretty easy to climb and it should take no longer than 20 minutes to walk up. The best time to climb is right before sunset and make sure to stay until the blue hours to see the city lights up.