Port: Tallinn, Estonia
This 125-foot-high cannon tower that dates from the 1470s has a funny name (translation: peep into the kitchen), and is home to a museum displaying weapons and other examples of medieval life. The tower is also where you can begin a tour of the limestone bastion tunnels of Toompea Hill.

Port: Riga, Latvia
Narrow cobblestone streets are off-limits to vehicles here, where many of the medieval buildings — destroyed by wars — were rebuilt during the late 20th century. Head to Town Hall Square to see the statue of Roland, patron saint of Riga, and the House of Blackheads building.

Port: Klaipeda, Lithuania
Hop a ferry from Klaipeda (Lithuania's only ocean port) to this stretch of sand that dates to prehistoric times. The UNESCO World Heritage site is home to delicate ecosystems including sand dunes, a lagoon, and pine forests, where deer and wild pigs roam. Don't miss the Hill of Witches, an open-air park dotted with wooden sculptures depicting Lithuanian legends, located in the resort town of Juodkrante.

Port: Helsinki, Finland
No, we don't mean choir numbers with electric-guitar accompaniment. This church, carved into the solid rock of the Helsinki peninsula, is an architectural wonder and popular concert hall (because of the neat acoustics).

Port: St. Petersburg, Russia
In the city of the czars, this impressive facility is the place to explore art and culture. Don't have time for more than three million works, including one of the largest collections of paintings in the world? Then start with the big-ticket items, like da Vinci's "Madonna with Child."

Port: Gdansk, Poland
This pedestrian street is Poland's equivalent to Barcelona's famous Las Ramblas. Dlugi Targ's centerpiece is the Neptune Fountain, with a history dating to 1549. The street is lined with impressive homes and historic buildings, including a palace and town hall, which was meticulously rebuilt after World War II.

Port: Copenhagen, Denmark
Pass on the Tivoli Gardens amusement park and instead check out this stunning waterfront royal residence. The complex dates to the 1750s and comprises four identical Rococo palaces on an octagon-shaped courtyard, with a circa-1771 equestrian statue of King Frederik V in the center. Stick around for the changing of the guard at noon.

Port: Stavanger, Norway
A hike to this huge flat rock on the Stavanger fjord gives you an incredible view from about 2,000 feet above the sea, and the scenery serves as a reward for the trek along the well-marked trails.

Port: St. Petersburg, Russia
The oldest church in St. Petersburg (early 1700s) is infamous for its prison cells that held noted Russian writers and dissidents. The fortress is the resting place of many czars, and you'll easily recognize it from its spire that rises high above the onion-domed skyline.

Port: Stockholm, Sweden
The official residence of the King of Sweden, this huge Baroque-style palace at the water's edge is open to visitors year-round. Inside, spend a full day touring the three museums, which fill more than 600 rooms among seven floors.