SecondLife is a 3-D Virtual Environment that is a combination communication platform, game and social gathering site.
Here's Wikipedia's introduction:
Second Life is an online virtual world developed by Linden Lab. It was launched on June 23, 2003. A number of free client programs, or Viewers, enable Second Life users, called Residents, to interact with each other through avatars. Residents can explore the world (known as the grid), meet other residents, socialize, participate in individual and group activities, and create and trade virtual property and services with one another. Second Life is intended for people aged 16 and over, and as of 2011 has about one million active users.
Some more pictures from previous a previous hosting location, Sunset River:
Jefferson Statue and Memorial
Tiki Themed Dance/Concert Floor
NRA Headquarters with Shooting Range