Where is it?

Tallinn - is the capital of independent Estonia. No problem to get in (at least - before 2020). If you are Saint-Peterburger and have a valid Estonian visa you can get the bus to Ivangorod, go through two checkpoints and two customs, cross the former "Friendship Bridge" to Narva, get the bus or train to Tallinn and vu à la - you are here less than one day...