Open Debug Menu
Press [Ctrl]+[Alt]+[D] while in-game to open debug options. Here you can control various things such as turning on wireframe mode, or making invisible objects visible. Note any change you make will have no effect on other players. To disable debug, press [Ctrl]+[Alt]+[D] again.
Press [Ctrl]+[Alt]+[V] to enable the admin menu, typically only useable by Lindens, and SIM owners. However enabling this allows you to locate anyone on the map, and send teleport requests to people who are not on your friends list.