Google often inserts little hidden jokes or features, known as Easter eggs, into its products.

Simply pressing Ctrl+Alt+A on Google Earth will take you to a flight simulator which you can fly anywhere in the world. Although it was initially an Easter egg, it has become a one of the official features of the software. 

The 3-D buildings on Google Earth are created by independent designers, who can add in their own personalized Easter eggs. If you spin around to the waterfront side of Sydney Opera House in Australia, you’ll find a model of the late crocodile hunter Steve Irwin. 

Although Google Earth has some of these easter eggs, some of the most famous ones have to do with their core product: search. Here's a list of some of the most famous search easter eggs that Google has had in recent years. Search for: 

• Anagram
• Do a barrell roll
• Recursion
• Tilt
• Askew
• Santa Claus
• Hanukkah
• Kwanza
• Binary 
• Zerg rush

Try them and see if you can explain some of them in the comments :)

(Source)