Ecotourism is alive and kicking on St. John. There's more than enough to do on land, from watching for wildlife in the national park to hiking miles of trails or strolling sandy white beaches. Hit the water for amazing snorkeling, swimming, even underwater photography—of course. This is the Caribbean, after all.

History lovers should know that Milan is not all about trendy shops and designer clothes. Among the city's many historical attractions are La Scala Opera, the Milan Cathedral, the National Museum of Science and Technology and Santa Maria della Grazie, the church that preserves da Vinci's "Last Supper".

Known as Padova in Italian, Padua may be the oldest city in northern Italy, if you believe the claims of its 12th-century BC founding by Trojans. It certainly has history, including its famous university (one of Europe’s oldest, from 1222), the 13th-century Basilica di Sant'Antonio (resting place of St. Anthony), and Scrovegni Chapel, with Giotto’s famed 14th century frescos. The magnificent Prato della Valle, a 950,000-square-foot elliptical square, is thought to be Europe’s second-biggest.

Sardinia’s largest city (with a little over 150,000 people) and its capital for centuries, Cagliari on the island’s south coast offers the perfect mix of recreation and exploration options. The five-mile-long Poetto Beach is among the best city beaches on the Mediterranean, and together with the adjacent Marina Piccola, satisfies all manner of sun and sea pursuits. Seekers of culture will love Cagliari’s old district, Castello, where 13th-century towers still guard the medieval city walls.

Golden domes, imposing white facades, and landscaped green spaces dominate the riverside streets of Rostov-on-Don. Though rich in history and culture, the port city is far from a relic—lively markets, theatres, and sports attractions give the metropolis its modern edge.