Tallinn has well preserved compact medieval old town, passable in 20-30 min by foot. See more: https://www.visitestonia.com/en/where-to-go/tallinn
Tallinn is the candidate for the title of ”european green capital” /EU Comission in 2022. Did you know, that BOLT is born in Estonia? As visitors of Tallinn you have everything you need in pocket – personal mobile phone and right apps for e-scooters, e-bicycles etc. Your operative “journey” planner – https://transport.tallinn.ee/#plan//en Modern+quick+free public transport service between airport/harbour and city is available.
See you in Tallinn!