For me it was impressive anything related to local Lithuanian culture since there is so little to see or do
I guess St Casimir fair left the biggest impression on me because there were so many people in the city (although it was freezing cold outside) selling all that traditional stuff like verba and medolis.
Day of the Restoration of the State of Lithuania impressed me the most because the vibe of Lithuanians. It was strongly felt, you know, all that unity and pride
Gates of Yotva (Yotvos Vartai) it's like travelling back in time
UZGAVENES, because the snow was so beautiful in Rumsiskes!