Tallinn is the capital city of Estonia and is one of the best-preserved medieval cities in Europe. This makes it a UNESCO site. It being a well-fortified city meant that it was never razed and pillaged during the medieval period. However, it was not so lucky during WWII when it suffered bombings from Soviet forces, but it still retains its charm.
The Ferry
A quick boat ride from Stockholm is this capital city that retains its medieval charm. From Stockholm, there are ferries that can take you all over the Baltic, for a relatively good price. I recently wrote an article calling it a travel hack. It is a 2-day trip, where you arrive at the boat prior to 5 pm, stay overnight, arrive in the city the next morning and stay for 6-8 hours and then get back on the boat to return around 10 am.
The total cost of the trip, which included 2 sets of meals (breakfast and dinner) at the all-you-can-eat buffet for 2 people sharing a cabin was 229 Euros. The most frugal part of the trip was that we did not have to pay for an additional hotel room since we had a place to stay. We also did not have to worry about finding places to eat as we knew we would have a set place to dine for four meals.
It is one of the most frugal ways I have calculated for traveling in the Baltic. We also got to see Tallinn in a relaxed manner since we did not have to take into account travel to and from the airport. The ferry took us right into the city and it was a 10-minute walk to Old Town Tallinn.
The city
Tallinn is an old fortified medieval city where many of the walls and towers are still standing. This consists of an Upper and a Lower Town. As the names suggest one is higher than the other.
The Upper Town is also known as Toompea which is at a defensible position, overlooking the town. This area has several sites, including Alexander Nevsky Orthodox Cathedral, and Toompea Castle. We did not make it to the Castle, however, the cathedral is a site that is not to be missed.
In addition, since this area is elevated you can get a bird-eye view of the Lower Town. The viewing platforms are called: Kohtuotsa and Patkuli. You do not want to miss if you are looking for the perfect Instagram shot.
Alexander Nevky Cathedral 
One of the many gates separating the two parts of town
The Lower town is known as All-linn, which has the majority of the medieval sites. This area includes the town hall square and the famous medieval walls and towers. Additionally, there is St. Olafs church where it was the tallest building in the 16th and 17th centuries. It does make an appearance in many of my photos taken throughout town.
The town square 
St. Olafs church 
The medieval wall and its towers
Further recommendations to travel the Baltic
One of my biggest recommendations for people who want to travel the Baltic is to choose one of the countries within it as your ‘home’ base and then take the ferries to each one of them. Stockholm is the most expensive of them, however, it has the most options. As you can go to all the Baltic countries, including Poland, even Russia via St. Petersburg. The latter of which cannot be taken on a day-trip as it only goes a couple of times a week. It does stop in Helsinki, so you can make a trip consisting of Stockholm-Helsinki-St. Petersburg.