Great Coastal Gate and Fat Margaret tower
They were built not only to defend the city from the seaward side of town, but also to impress any visitors arriving via the harbour.
The Great Coastal Gate, along with the Viru Gates, are the last of six gates that controlled access to the town in Medieval times. The gate system here on Pikk street originated in the 1300s, but it was during reconstruction in the early 16th century that the Fat Margaret cannon tower was added. Built from 1511 to 1530, this hefty, round tower has a diameter of 25 metres, a height of about 20 metres, and walls up to 5 metres thick.
The origins of Fat Margaret's name are a mystery. Some theories insist it was named for one of its larger cannons, while others hint at a cook called Margaret who once worked here.
In any case, the tower has served a number of different functions throughout its history. It has been used a storehouse for gunpowder and weapons, and as a prison.
Now it's home to the Estonian Maritime Museum, which provides a detailed look at the nation's seafaring past.
Visitors should be sure to climb up to its rooftop viewing platform to get a lovely view of Old Town and the bay.