Skybox

Second Life: A floating home or business that can be positioned at any altitude up to 4,000 meters, reached either by teleporter or flying. Many people in Second Life "live" in skyboxes, which range from simple, unattractive boxes to complex castles to ornate architecture from various periods to urban lofts with 3D image windows. Skyboxes stay up indefinitely and don't fall unless you want them to (by making them physical so they react to forces, including gravity).

It's a lot of fun breaking into people's skyboxes and using their beds for trespass slex. Just be fast with the Shift-CTRL-H to get out of there quick if someone comes home and catches you in their bed!