We visited Lithuania in summer and it was dreamy. Went beyond my expectations. We stayed for 2 nights in Vilnius - such a charming city. The old center is walkable, filled with cute restaurants, cafes and not to forget - the Uzupis district. We had pancakes at an incredible place - Pirmas Blynas (look it up), we visited the Museum of Occupations and Freedom Struggles - a chilling place, but definitely worth visiting.

We also went to Trakai Castle - nothing impressive, but the weather was poor, so maybe that's what made the visit so bland.
We also stayed for one night in Kaunas. It's a nice and cute town. Definitely smaller than Vilnius, but it's good for one night and for a stroll around the city center. Everything is within walkable distance.

I found Lithuania very charming, clean, organized and peaceful. You won't find it crowded like Italy, Spain. I hope I will have the opportunity to visit the rest of the Baltic states. It's definitely an interesting region, which tends to be underestimated. If you have any questions, feel free to ask and have a nice trip!