Radegast is a light weight viewer for LLLP compatible virtual worlds (Second Life(r) and OpenSimulator in particular). It allows one to log in, chat, see maps, operate on your inventory and list the objects about one.
Radegast is extensible with plugins and LookingGlass has a Radegast plugin interface. Below is mentioned a zip file that one extracts into the Radegast bin directory. Then, when Radegast is run, a "LookingGlass" item shows up in the "Tools" menu.
When you press the "LookingGlass" menu item, wait a few seconds because it takes time to load the simulator state from Radegast into LookingGlass. After a bit, the LookingGlass viewer window will appear and the sim your are in will be displayed.
On the Radegast chat page, there are some navigation buttons in the lower right corner. Pressing these will move the avatar and change the view. If you use the map function to teleport, the new sim will be displayed.
General LookingGlass configuration is not done with the usual LookingGlass.json file but the file RadegastLookingGlass.json file is used when LookingGlass runs under Radegast. The main differences are a slightly different module definition (doesn't use the regular LookingGlass communication module since Radegast already has one) and a different UI class (to rely on Radegast's UI). In most other ways, the normal configuration rules apply.
Binaries for LookingGlass are available on it's home page. The binaries are created for the latest Radegast on a regular basis.
If you are building LookingGlass from sources, there is the script trunk/bin/RadegastCopy.sh which will copy the required files into the Radegast binary directory. Inspect that script, modify for your system and use.