Gardening is an activity usually enjoyed in the bright light of day. But for a certain group of green thumbs, the digging is done in the dark.

“Guerrilla gardening” is a growing movement around the world, with its roots in both environmental friendliness and community beautification. Illicit cultivators set their sights on barren ground—most often in rights of way or vacant lots. Under cover of night, or at least when no one's looking, they wield their shovels and watering cans and turn empty plots into urban Edens.

Sometimes, the rogue planters' actions can be disruptive—in May 2000, thousands of them took over London's Parliament Square, planted vegetables and flowers everywhere, and even gave the statue of Winston Churchill a green Mohawk. Most often, however, the random acts of greenness are seen as harmless, or even beneficial. After all, an abandoned square of ground can be an eyesore, or a prime place for mosquitoes or other health risks to thrive, whereas wildflowers and other plants are nicer to look at, and stormwater friendly.

In 1973, New York City's Green Guerrilla Group descended upon an abandoned lot and planted the heck out of it—today, the plot is still flourishing, but under the protection of the city's parks department.

For more information, visit www.guerrillagardening.org.

Sewer tour shows another side of Paris

Ah, Paris. Known the world over for its fine wine, exquisite cuisine, and...sewers?

The Musee des Egouts de Paris—or the Paris Sewer Museum—offers visitors to the City of Lights the chance to tour its wastewater system. In addition to an exhibition area that displays artifacts and audiovisual presentations on sewer technology through the years, the museum also offers a tour that gets right down into the city—literally.

The average tourist might turn his or her nose up at the attraction, but for infrastructure aficionados—and for fans of Les Miserables, in which the Paris sewers play an important role—it's a gem. Visitors get to see what was once the main line between the Place de la Concorde and the Pont de l'Alma, historic sewer-maintenance gear, and much more.

Vive le sludge.