Visit Vilnius Cathedral
One of the most prominent landmarks that you will likely see the moment you arrive in Vilnius is Vilnius Cathedral, a classical-style Roman Catholic Cathedral that was constructed in the 18th Century over a Pagan temple. During the Soviet reign, it was converted into a warehouse until 1988 when Lithuania gained independence and converted back into a cathedral that anyone can enter.
You can climb to the top of the Gediminas Castle Tower for a breathtaking view of the Old Town and all of its lovely orange roofs by paying 5 EUR, but you can also take in the view from the bottom of the tower for free. In either case, ascending the hill is essential if you want to gain a breathtaking view of Vilnius.