Royal Greenhouses, Flanders

Completed in 1873, the Royal Greenhouses on the grounds of the Royal Palace of Laeken in Flanders, Belgium, were built to resemble a glass city, with rotundas and cupolas harboring exotic plants, some of which were brought back from the Congo.

Each year, while the azaleas are in bloom, the Royal Greenhouses are open to the public for three weeks only. In 2015, they will be open April 17-May 8. Entry costs €2.50. Tickets cannot be purchased in advance. Contact the Flanders tourism office (phone +32 0 2 513 89 40, www.visitflanders.us).