City wall and watch tower in San Juan, Puerto Rico (@ Zhang Jun/Xinhua Press/Corbis)

City wall and watch tower in San Juan, Puerto Rico (@ Zhang Jun/Xinhua Press/Corbis)

comments,

Sheepdog guards a flock of sheep in the Tatra Mountains, Poland (@ Henryk T. Kaiser/Age Fotostock/Photolibrary)

Sheepdog guards a flock of sheep in the Tatra Mountains, Poland (@ Henryk T. Kaiser/Age Fotostock/Photolibrary)

comments,

Interior of the Sydney Opera House, Australia (@ Hervé Hughes/Corbis)

Interior of the Sydney Opera House, Australia (@ Hervé Hughes/Corbis)

comments,

Icelandic horses running through a lagoon in Iceland (@ Tim Flach/Getty Images)

Icelandic horses running through a lagoon in Iceland (@ Tim Flach/Getty Images)

comments,

Freshwater ectoproct bryozoan (Cristatella mucedo) (@ Wim van Egmond/Corbis)

Freshwater ectoproct bryozoan (Cristatella mucedo) (@ Wim van Egmond/Corbis)

comments,

Astronomical clock on the Zytglogge tower in Bern, Switzerland (@ Blaine Harrington/age fotostock)

Astronomical clock on the Zytglogge tower in Bern, Switzerland (@ Blaine Harrington/age fotostock)

comments,

The twin peaks of Mount Ushba in the Greater Caucasus mountain range (@ Brooks Kraft/Corbis)

The twin peaks of Mount Ushba in the Greater Caucasus mountain range (@ Brooks Kraft/Corbis)

comments,