Museum
Signatories House (The House of Signatories)
2 locals recommend,
Tips from locals
The whole Lithuanian struggle on breaking out of the Soviet dictatorship is told there. There is also the re-discovered declaration of Independence on display too. Part of the musuem is free, part is paid (~3-5 euros, if I remember correctly).
Unique things to do nearby
Location
26 Pilies g.
Vilnius, Vilniaus apskr.