On March 19, dozens of countries around the world observed the 10th annual "Earth Hour."

Famous landmarks around the world — and millions of private citizens — turned off their lights for 60 minutes at night to create stunning, rarely seen images of their cities.

1. Here's the Parthenon in Athens, Greece, with its lights on...

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This incredible art project in Paris uses heartbeats to plant trees. Here's how.

The Eiffel Tower knows how to go green and looks great doing it.

Plenty of folks have seen the Eiffel Tower.

Photo via iStock.

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Natural Resources Defense Council